tag:blogger.com,1999:blog-86700657497619401872024-02-21T05:11:53.066-08:00Get Into PhysicsDr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.comBlogger60125tag:blogger.com,1999:blog-8670065749761940187.post-12271697497093756122012-03-06T05:10:00.000-08:002012-03-06T05:10:24.152-08:00A Voice That Could Break Glass<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">My sister. No, she doesn’t have a voice that could break glass. But she does have an inquiring mind combined with an idea that Physics is probably just a conspiracy. I’ve no idea why she suddenly decided to text me early on Sunday morning asking if you could break glass with sound, but she did. She was so suspicious of my texted reply that I needed to elaborate - so here is my answer.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Let’s start with sound waves. We know that of the two types of waves, transverse and longitudinal, that sound waves are longitudinal. That means that the sound source vibrates backwards and forwards and moves the air molecules accordingly.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9hBz6vaSPHjMLImv6kpyr9BXnEe4CXw6hQqNZus8poDuZwYwmGBbPnlJVIVSQVshPKpHwbfIUcpQoA9Ur3X18UCzR70m0vDjM7BpNsNO29wBgXYPy0Q9TaazDrrnX7_53ydQnVOsK1mE/s1600/img1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="263" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9hBz6vaSPHjMLImv6kpyr9BXnEe4CXw6hQqNZus8poDuZwYwmGBbPnlJVIVSQVshPKpHwbfIUcpQoA9Ur3X18UCzR70m0vDjM7BpNsNO29wBgXYPy0Q9TaazDrrnX7_53ydQnVOsK1mE/s400/img1.png" width="400" /></a></div> </div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Under normal circumstances though, these sound vibrations can’t really move much apart from your ear drum, this being how you hear the sounds. There are a number of things you can measure that tells you more about the waves – the amplitude, the wavelength and the most important one here – the frequency. The frequency means how many waves per second there are and this is measured in Hertz. The higher the frequency, the higher the pitch of the noise that you hear.</span><br />
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</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhxmrnlJ37G3oCcfcVvBj3MiT3mWr8dgQActdP9YtHiETG6cMKImXiIPjXCBB4A66BWkimtsUadAzJk7UHWNCQXHUkbS2idOuumn9R7KAAHR2TlcPc9u9n4BgJydG7lwKpbPiJIzUA0Y1c/s1600/img2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="263" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhxmrnlJ37G3oCcfcVvBj3MiT3mWr8dgQActdP9YtHiETG6cMKImXiIPjXCBB4A66BWkimtsUadAzJk7UHWNCQXHUkbS2idOuumn9R7KAAHR2TlcPc9u9n4BgJydG7lwKpbPiJIzUA0Y1c/s400/img2.png" width="400" /></a></div><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">So, we know that for most frequencies, sound cannot break glass. We know this from our everyday lives – the glass we drink out of, the glass in the windows, they don’t just spontaneously shatter on a regular basis, not even when someone really annoying talks right by them.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Ok, a small aside. You know how when you’re swinging on a swing, if you get your legs helping you just right then you’ll keep getting higher and higher, but if you get your legs wrong it’s impossible? That’s all about working with the frequency that the swing naturally wants to swing at and not trying to make it go faster or slower.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">The same is true with sound waves and breaking glass. Once you get the right frequency, what starts off as teeny tiny vibrations of the air next to the glass and then the glass itself, if you can get the waves pushing at just the right time, the glass will start to vibrate, then ripple more and more and more. This is called the resonating frequency.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Obviously, glass is a brittle material, but when you get it at its resonating frequency it almost looks like it’s acting like water. Well, that’s until it smashes! After all, it’s still glass.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Fancy checking this out? Search youtube for "resonating sound breaking glass" and there are some great examples!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-53470858341688569622012-02-17T05:16:00.000-08:002012-02-17T05:16:39.792-08:00A Bit Dim<div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjeZcKrrTA6PxR8j3TZgyKjTpDbQK1vL4BMzJscu2epgUILdWI02MOkXxKMomGu5gbSclYmGtKgUug5aF-HHB70qU6Fbu-4naBx7vGsNL5gq4TKC2AyVev4eGMIu6z3hhqHOkgXInAzYPM/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="263" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjeZcKrrTA6PxR8j3TZgyKjTpDbQK1vL4BMzJscu2epgUILdWI02MOkXxKMomGu5gbSclYmGtKgUug5aF-HHB70qU6Fbu-4naBx7vGsNL5gq4TKC2AyVev4eGMIu6z3hhqHOkgXInAzYPM/s400/fig1.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Light switches – have you ever noticed that some of them just let you switch the light on and off, whilst others give you the power to choose how bright you want the light to be? How they do this is pretty simple, so let’s look at it a bit more closely.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">We’ve previously covered resistance <a href="http://getintophysics.blogspot.com/2011/05/resistance-is-futile.html">here</a> in electronic wires, with the contributing factors being 1) material type 2) wire length 3) cross-sectional area 4) temperature. So let’s think which of these we can change of a varying basis depending on what brightness we want.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">It’s a pretty costly solution to have different wires made from different materials running all round your house just in case you want to dim the lights, and it would be hard to get a continuous scale too. Likewise cross sectional area would require a huge amount of extra wiring. That leaves us with temperature and length.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Whilst I like the idea of changing the brightness of a bulb by changing the temperature, it seems a little impractical! So that leaves us with length. You need quite a lot of wire to change the resistance so dramatically that you will notice it in the brightness of your bulb, but the dimmer switch is usually just a rotating knob. The wire is coiled up on itself so that rather than being able to choose from any point along its length, you make contact with one spot along the coil.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgJ_UywRvDZLwoAUvdFrv06slHgA_A6AYBngFXLP-bYNbtpksnU6epXpenMsl4Q8ft_rtDd6_nBHtBPoZUt2ij7N2tTRXNfKS80C49DQ_C1_0VbxorLEpECtjrunqHQOjJiVFc9xkAUnRA/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="263" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgJ_UywRvDZLwoAUvdFrv06slHgA_A6AYBngFXLP-bYNbtpksnU6epXpenMsl4Q8ft_rtDd6_nBHtBPoZUt2ij7N2tTRXNfKS80C49DQ_C1_0VbxorLEpECtjrunqHQOjJiVFc9xkAUnRA/s400/fig2.jpg" width="400" /></a></div><br />
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</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">That way you get a lot more change in resistance with only small turns of the dial - meaning that rather than a huge distance moved you can just use a rotating switch. This type of resistor is called a variable resistor and its symbol is:</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgTx1Sj4EWNlSQLSGGc0DEW7EgpKgG3Gq7g6CUXgmeURwQzczBDBgeNCZmd7SwCq6bfZh3vKx12Ae7SqU3eIeHwCysvP4jU46gkjllMGbWWxNXJzSisZBHoBrR0MrT4ynOCVYsBj1BpJso/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="211" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgTx1Sj4EWNlSQLSGGc0DEW7EgpKgG3Gq7g6CUXgmeURwQzczBDBgeNCZmd7SwCq6bfZh3vKx12Ae7SqU3eIeHwCysvP4jU46gkjllMGbWWxNXJzSisZBHoBrR0MrT4ynOCVYsBj1BpJso/s320/fig3.jpg" width="320" /></a></div><br />
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</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">It’s used for other applications too, can you think of any?</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-38678238749794839372012-02-07T05:08:00.000-08:002012-02-07T05:08:41.765-08:00Precision Counts<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Watching the TV the other night, I was confounded by an advert that promised “the search for fast”. And I thought, shouldn’t that be “the search for speed”? Now, I know that arguing with the TV is pointless, and definitely always ends up with you looking a bit mental and nothing resolved, but this one really stuck in my brain.</span></div><div class="MsoNormal"><br />
<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgDTYjtVqSQvnnzvjCNF8MkktR8HM3LkF3uQe2cSq1FI05iHpAzLxEEXbbRFTGq-xgosNweh1Db70Hjgaa3JM8RHc3qjb2Yq81VrH_RBud_siG7TaGvAiCMmKms25O0LiaYgz9YuNGO_TA/s1600/fast.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="265" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgDTYjtVqSQvnnzvjCNF8MkktR8HM3LkF3uQe2cSq1FI05iHpAzLxEEXbbRFTGq-xgosNweh1Db70Hjgaa3JM8RHc3qjb2Yq81VrH_RBud_siG7TaGvAiCMmKms25O0LiaYgz9YuNGO_TA/s400/fast.jpg" width="400" /></a></div></div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">What is fast exactly? As a scientist, it’s a loose term you can use to describe how someone or something moves, eg that car is moving fast. But it doesn’t really tell you anything, since it’s relative. If the car were overtaken by a train, you might say that the car is still fast but the train is faster. But that’s not really the whole of the story.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">When it comes to science, it’s not just numbers that you need to worry about – words are important too. They can tell you a lot about the problem that you’re trying to solve so pay attention! I’ve spoken several times about the difference between speed and velocity, with speed being a directionless way of measuring how fast something is going, whilst velocity is also about direction.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">What that means in practical terms is that if you imagine a car going around a race track at a steady speed of 50 mph, the velocity will be changing as the track twists and turns. This can be a confusing concept to start with, but once you get to grips with this and other important distinctions in the language of science, you’ll start to see things in a new light.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Start by thinking about what the difference is between weight and mass for example (hint, one of them changes with gravity and one doesn’t) or between force and weight.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Ok, so becoming a bit picky and precise about words might lead you to rant about an advert and its search for “fast”. What is that? And how do you search for it?? But at least you’ll be thinking critically about what words to use to accurately describe things, and that will make me glad. </span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-974024719757810582012-01-17T05:10:00.000-08:002012-01-17T05:10:57.177-08:00Absolute Zero<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">You might think that it’s been pretty cold the past few days, especially compared to the warm wintry days we’ve been experiencing recently, but what’s the coldest weather you’ve ever felt?</span><br />
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<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgb_m4c6ckOuE1gKbSEIT-i-slvaTCtY6M8_rknPSDWIYxgE0058P54o398sPKYLFcxcl4xg8vmqyfhm3nJC078uheD9PNs9OpoDywpFglgTln5XEJ_QJb1ktaU3vCb5gjOfb9hvpkAAG8/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="265" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgb_m4c6ckOuE1gKbSEIT-i-slvaTCtY6M8_rknPSDWIYxgE0058P54o398sPKYLFcxcl4xg8vmqyfhm3nJC078uheD9PNs9OpoDywpFglgTln5XEJ_QJb1ktaU3vCb5gjOfb9hvpkAAG8/s400/fig1.jpg" width="400" /></a></div></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">I’ve probably been in around -10°C, possibly a little colder, although not usually being in the habit of carrying a thermometer with me I can’t say for absolute certain. Most of us, unless we visit the Arctic or climb Mt Everest won’t get the chance to be really really cold, like -40°C.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">And yet, there’s still colder, so cold that there’s another temperature scale to make it easier to understand and write about. In the UK we usually use Centigrade to measure temperature, although the older generation often prefer Fahrenheit. These have a complicated relationship and it’s hard to translate one into the other in your head.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">The Kelvin scale (symbol °K) starts at absolute zero, the coldest possible temperature, at which even atoms stop their constant vibrations. It’s the same as the Centigrade scale but starts at -273°C. We’ve (well, not me personally, scientists ) managed to measure to within 0.000000000000001 degrees of absolute zero, which is pretty close in my book!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-19800436293728842762012-01-13T05:13:00.000-08:002012-01-13T05:13:16.042-08:00Skating on Water<!--[if gte mso 9]><xml> <o:OfficeDocumentSettings> <o:AllowPNG/> </o:OfficeDocumentSettings> </xml><![endif]--><!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:TrackMoves/> <w:TrackFormatting/> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:DoNotPromoteQF/> <w:LidThemeOther>EN-GB</w:LidThemeOther> <w:LidThemeAsian>X-NONE</w:LidThemeAsian> <w:LidThemeComplexScript>X-NONE</w:LidThemeComplexScript> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> <w:SplitPgBreakAndParaMark/> <w:EnableOpenTypeKerning/> <w:DontFlipMirrorIndents/> <w:OverrideTableStyleHps/> </w:Compatibility> <m:mathPr> <m:mathFont m:val="Cambria Math"/> <m:brkBin m:val="before"/> <m:brkBinSub m:val="--"/> <m:smallFrac m:val="off"/> <m:dispDef/> <m:lMargin m:val="0"/> <m:rMargin m:val="0"/> <m:defJc m:val="centerGroup"/> <m:wrapIndent m:val="1440"/> <m:intLim m:val="subSup"/> <m:naryLim m:val="undOvr"/> </m:mathPr></w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" DefUnhideWhenUsed="true"
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<div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">Dr Em’s fun fact for Friday 13th: whenever you go ice skating, you actually skate on water.</span></div><div class="MsoNormal"><br />
</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4lmWSvhr-0faC4KUvwTnKhamzNcl2r1T16weuZkNidRSAWAl8tGSzSItxTKLfXhJ0cRddt4VprKnZEKSvA97JMCFnv-cdZZbhnITDRhKuh6XL5KkACpe21p5ujjnjKUvkUH1bh0b88M8/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="235" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj4lmWSvhr-0faC4KUvwTnKhamzNcl2r1T16weuZkNidRSAWAl8tGSzSItxTKLfXhJ0cRddt4VprKnZEKSvA97JMCFnv-cdZZbhnITDRhKuh6XL5KkACpe21p5ujjnjKUvkUH1bh0b88M8/s400/fig1.jpg" width="400" /></a></div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;"> </span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">Let’s break this down. Remember how your mum used to tell you that ice skates could cut people’s fingers off? That might be just a scare tactic or an excuse but there is some logic behind it. It’s all to do with the fact that ice skates have a very very small area that’s in contact with the ice. That means a very high pressure.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">If we say that the ice-skate blade is 25cm long and 1mm wide, we can work out the total area in contact with the ice.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">A = 0.25 x 0.001 = 0.00025 m-squared</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">Pressure is Force divided by Area so presuming that you weigh 60kg let’s find out the pressure. Assume gravity is 10 m/s/s</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">F = weight x gravity = 60 x 10 = 600N</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">So,</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">P = 600 / 0.00025 = 2400000 Pa = 2.4 MPa</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">That’s quite a large amount of pressure, certainly enough to melt the localised patch of ice underneath your blades. Of course, it freezes over again more or less as soon as you’ve passed, but the fact remains that you ice-skate on water.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">As for fingers, I think we need some volunteers to see whether 2.4 MPa is sufficient to remove one of those…any takers? On second thoughts, that sounds too much like Biology for me.</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-2435333702827217762012-01-10T05:17:00.000-08:002012-01-10T05:17:43.628-08:00Rock, Paper..Water?<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">As I was playing rock, paper, scissors the other day, I thought how stupid it was that paper beats rock. I mean, sure, it covers it…but that’s about all. So I was wondering if I could come up with a better trio to play the game with. And because all thoughts in my brain lead to science I thought I should share some of the match-ups I considered</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><b><span style="font-size: 12pt; line-height: 115%;">Rock v Water</span></b><br />
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<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXkor8ox29BwAK2_YlZiu1YXwDCyb_JyKsni0qXABKuxzugZtCrNTTQMrHRZtK1V7pQ6YiPL4GrVcXvd5Hi8MxWAC9ivyX7LcNrfITHtomcfnyCh2gsOVsw3DwliHhZqIx297bohS7CF8/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="201" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXkor8ox29BwAK2_YlZiu1YXwDCyb_JyKsni0qXABKuxzugZtCrNTTQMrHRZtK1V7pQ6YiPL4GrVcXvd5Hi8MxWAC9ivyX7LcNrfITHtomcfnyCh2gsOVsw3DwliHhZqIx297bohS7CF8/s320/fig1.jpg" width="320" /></a></div><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Seems simple, right? Rock goes in the water, and you could argue that the rock wins as it stabbed through the water, or that the water wins since it absorbed the rock. I’m thinking more technical though. When water freezes it makes ice, which we know takes up more volume than as a liquid (test this by filling a water bottle full and putting in the freezer, it’ll be all swollen). In cold places, water creeps down the holes in rocks, then when it freezes, pushes the rock apart, over time splitting huge bits of rock off. So, water most definitely beats rock then.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><b><span style="font-size: 12pt; line-height: 115%;">Paper v Chalk</span></b><br />
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<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjWBaOIN2eJ1HhExP-R92tSog60fSrEPDjIENCXd1cz8WG7HVpi37YnpnyLMWKVjac7XCuzPhTzDBzn8YHQXGfcYW6NZlaITQr_EyI02QY9EFdXWyINemNPHihJBDV4O9DVFi6WOK2wOew/s1600/fig+2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="201" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjWBaOIN2eJ1HhExP-R92tSog60fSrEPDjIENCXd1cz8WG7HVpi37YnpnyLMWKVjac7XCuzPhTzDBzn8YHQXGfcYW6NZlaITQr_EyI02QY9EFdXWyINemNPHihJBDV4O9DVFi6WOK2wOew/s320/fig+2.jpg" width="320" /></a></div><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Chalk writes on paper, paper gets written on, seems fairly straightforward that chalk wins. But don’t be so hasty! Have you seen those card throwers? Go on – look them up on youtube, I’ll wait. They have the ability to cut, pierce and slice with nothing but a playing card or business card and the right throwing technique. It’s all about the pressure that you can create with the card edge, and pressure comes from force. A flying card has plenty of forwards thrust thanks to the thrower, and combine that with the tiny area of the card edge and you can see how easy it would be to get the card to pierce something…like a piece of chalk. So, paper could win!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><b><span style="font-size: 12pt; line-height: 115%;">Water v Paper</span></b><br />
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<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiaP67eeh1li6SKSEAyQFGFPuHEpny-Zb4M6GRiT8CFpLrnoLg4QaFhgmHEWrICQkgQD2W087u6C6g7zd4GMo32lIhMC_UJ5dh-VZ3eLE6BqI6VCVffKEVhM7fgHDGT2hkBjYf2vgDeQAY/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="201" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiaP67eeh1li6SKSEAyQFGFPuHEpny-Zb4M6GRiT8CFpLrnoLg4QaFhgmHEWrICQkgQD2W087u6C6g7zd4GMo32lIhMC_UJ5dh-VZ3eLE6BqI6VCVffKEVhM7fgHDGT2hkBjYf2vgDeQAY/s320/fig3.jpg" width="320" /></a></div><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">If this was a game played with hands I wouldn’t like to try and guess how water would be done, but thankfully that’s not part of the problem I’m worrying about here! Paper goes in the water and gets soggy seems like too much of an obvious answer here. Let’s imagine we’ve got a piece of paper that won’t get soaked too easily, like a playing card again. Take a glass of water, put the card over the top and carefully turn upside-down. Now lift up the glass… Careful! You’ll find that the paper has trapped the water, thanks to the way that the water forms a seal and won’t let more air in, effectively creating a semi-vacuum that holds the water up.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">So it seems that rather than creating a new game that actually works, I’ve just been busy defending poor paper. Not just “wins by covering rock” but much more awesome than that, thanks to a few little bits of physics. Paper cuts rock (well, chalk) and paper traps water. Go paper! I’ll always choose you now. Just beware the scissors, there’s nothing that can save you there.</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-70947962049531578392012-01-05T05:21:00.000-08:002012-01-05T05:21:16.832-08:00Water Water Everywhere<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Rain and wind, that’s all we seem to get at the moment, morning, noon and night. Wouldn’t it be nice if we could actually benefit from the elements rather than just complaining about them? This is where renewable energy generation comes in. Unlike solar power, wind and rain are more frequently abundant when we need the most power, when we’re cold during the winter.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Wind turbines and hydroelectric power (the posh name for electricity from water) stations have their origins centuries ago when windmills and watermills were both used to process grain into flour, which is where the “mill” part of the name comes from. Turning your energy source into mechanical motion is a nice and efficient way of using the energy, but there’s no way of storing it or sending it elsewhere if you have too much to use.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj6OtWl15y5Yn_RtFthj6GZkHEwGYm7ERwAXycxzGIV0NzZEJysc6mUL-chE2-Cl2okcCLQ-rWfrhV28Rx3mj473wwRdNRwXiQg10MMIcOt5G76esW_F8uu8F86-LYThHNdjOtG95tKXGc/s1600/fig+1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="251" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj6OtWl15y5Yn_RtFthj6GZkHEwGYm7ERwAXycxzGIV0NzZEJysc6mUL-chE2-Cl2okcCLQ-rWfrhV28Rx3mj473wwRdNRwXiQg10MMIcOt5G76esW_F8uu8F86-LYThHNdjOtG95tKXGc/s400/fig+1.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">So turning the power of wind and water into electricity makes it much easier to share, although it’s still pretty tricky to store. Good job it seems to be windy and rainy all the time then! But how do we go about getting electricity from the wind or the rain? It’s not like you can just hang your plug out of the window and get it that way!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Remember how we learned about getting electricity from fossil fuels (<a href="http://getintophysics.blogspot.com/2011/09/fair-exchange-is-no-robbery.html">previously</a>)? Well this works just the same, but rather than burning the fossil fuel to make steam to turn the turbines, the water or the air turns them directly.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjvuCvZSvdp8KhWOUk5T5qh0Je53VBNznIIVdlTcM2WFC_wgmt68TnKjFW3t9vgmXpdfZ-3zpEyYsIe6ejFMcdzGyfS9qg9yP_rUm59UFS3PrvSqJBdjY7VvEJDUzXGbpTgvM7jOxaahts/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="251" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjvuCvZSvdp8KhWOUk5T5qh0Je53VBNznIIVdlTcM2WFC_wgmt68TnKjFW3t9vgmXpdfZ-3zpEyYsIe6ejFMcdzGyfS9qg9yP_rUm59UFS3PrvSqJBdjY7VvEJDUzXGbpTgvM7jOxaahts/s400/fig2.jpg" width="400" /></a></div><br />
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</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">This can be problematic though, because whilst you can accurately control the steam pressure when you’re burning the fuels, there are no such controls on the elements. It’s usually a trade-off between getting some power out when there’s not such a high flow, and making sure that you don’t have the turbines running too fast when the winds are howling or the water is racing.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Wind turbines are often geared towards moderate winds, so you’ll notice that sometimes when it’s too windy that the turbines are switched off. This is partly for health and safety but also because they just can’t cope when the gusts are really racing, but they can generate electricity in all but the most still conditions.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Water is easier to control, because you can build dams, but that can get costly and people don’t tend to like it when you flood the valley that they live in! There are also many more types of water powered electricity generators, with things like power from the tides, underwater currents in the sea, and storm water becoming increasingly likely to be a big player in the future of renewable energy. </span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-37463728840017291402011-12-08T05:20:00.000-08:002011-12-08T05:20:30.993-08:00Eureka!<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Eureka is the well-known shout of Archimedes, uttered when he had his great idea about mass, volume and water, apparently when he got into the bath and it spilt over the edges.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">He realised that when you get into the bath, water is displaced – you take up the space of the water. Now, this may not seem all that huge to us, but back then when they were just starting to figure things out that still form the basis of our scientific ideas, this was a big deal!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">If things are more dense than water, they sink. This means that the water that they displace is equal to the volume of the object. This is a great way to measure volume of irregular shapes that are tricky to calculate otherwise, like rocks.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgAWRGrz_Mk6OFnMejShoUSrngMemybrpIh-zL7MEHFfT4ivrumisF1A459tFWR6vUlqP1RRiWwEuIFYetyRk91aX6jW2UXJKmG4hWZ00YG1Z1UdC_KituH73Bv5xHB_RC8RYfKah_CLCk/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="251" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgAWRGrz_Mk6OFnMejShoUSrngMemybrpIh-zL7MEHFfT4ivrumisF1A459tFWR6vUlqP1RRiWwEuIFYetyRk91aX6jW2UXJKmG4hWZ00YG1Z1UdC_KituH73Bv5xHB_RC8RYfKah_CLCk/s400/fig1.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">If the object floats, or is partially submerged, then you can discover the mass. Now, I know that’s not all that amazing in this day and age with digital scales and even the ability to weigh objects when you’re playing on the Wii, but bear with me, since this was pretty important.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhDd8IX4ogEykymurmoMahcbHaIQzSgvY4nKCqFm674bD6zN49E6Yuf3pQVM5gWPdGFDMU2i5_2N8Uj7cPNgEk7MwSXFkYjsJJGy6lJf4FUrs-Mn7hjZ1p7uDdKiwFt-5Fm4j8xrhrnj14/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="251" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhDd8IX4ogEykymurmoMahcbHaIQzSgvY4nKCqFm674bD6zN49E6Yuf3pQVM5gWPdGFDMU2i5_2N8Uj7cPNgEk7MwSXFkYjsJJGy6lJf4FUrs-Mn7hjZ1p7uDdKiwFt-5Fm4j8xrhrnj14/s400/fig2.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">When something floats, the volume of water displaced is equal to the mass of the object, as the forces equal out, the mass of the object equalling the pressure increase thanks to the water displacement.</span><br />
</div><br/><br />
<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">The only thing that this principle doesn’t take into account is surface tension, which we know is an important phenomenon. Surface tension means that it’s harder to break apart the bonds at the surface of the water, so if you are careful, you might just be able to sit small (and flat-ish) objects on the surface to test out how strong this is! Start with an autumnal leaf, try paper ships or even a piece of card that you can balance things on to see how much it will stand!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-27345026483054335562011-12-06T05:22:00.000-08:002011-12-06T05:22:25.433-08:00Wear A Vest!<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">If your grandmother is anything like mine, the moment the frost hits the ground she’ll be calling you up just to check you’re wearing a vest! I’m sure she just wants me to be warm, but at the ripe old age of *cough splutter* I find myself capable of dressing myself!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidOJEBfRCJh7GXBSwLS7-Bcg2TWJDM1yc0antyBDXq3_-4byOTbiNcR7NFU-2YjpA5cFmKJALpJ6z_2wSTgAU8op04RAZteKGQmUWSpsaklTaY8iLbL9SrSHvoyIuue9HMvRGlEBSygE4/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="290" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidOJEBfRCJh7GXBSwLS7-Bcg2TWJDM1yc0antyBDXq3_-4byOTbiNcR7NFU-2YjpA5cFmKJALpJ6z_2wSTgAU8op04RAZteKGQmUWSpsaklTaY8iLbL9SrSHvoyIuue9HMvRGlEBSygE4/s400/fig1.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">But maybe there is something in this vest stuff? Why are they good to wear? Well, it’s because more layers of clothing mean more trapped air layers between you and the outside. Which doesn’t sound all that wonderful until you think how bad air is at conducting heat. Sure, it’ll move heat around by convection, but there’s not really much space under your jumper for a breeze to start up!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">As we learned before <a href="http://getintophysics.blogspot.com/2011/11/conducting-show.html">here</a> heat travels by three main methods, convection, conduction and radiation. A layer of air between the hot surfaces and the cold means that these three effects are minimised. Air is an insulator because it doesn’t conduct heat very well. Sure, there are better insulators out there, like roof lagging, but that certainly doesn’t make for an attractive or comfortable outfit!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">And just as we can heat ourselves up with a vest to trap air, we do the same to our houses. Double glazing is the architectural equivalent of a vest, with the two panes trapping all that insulating air inside to protect you from the cold.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgssfqSYBTlYrLuP8E_rO5JlQU_M_07h_VtdlmRi-Lh5hdj4Mojc-4sIGWvIymNXXOAtYUo6ZHwYn9nokUvweajP0kAIh0nbFijDaRWJX6xZ9CnWvefJjHaVVB9mK9fHJCQ7eB9-gpSvmQ/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="290" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgssfqSYBTlYrLuP8E_rO5JlQU_M_07h_VtdlmRi-Lh5hdj4Mojc-4sIGWvIymNXXOAtYUo6ZHwYn9nokUvweajP0kAIh0nbFijDaRWJX6xZ9CnWvefJjHaVVB9mK9fHJCQ7eB9-gpSvmQ/s400/fig2.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">If you don’t have double glazing, you can also make it yourself, although take this as a warning that people like to poke holes in it for fun. Simply take cling film, stick to the edges of the windows and fill in the centre leaving your insulating layer of air trapped. Apply gentle heat with a hairdryer to shrink to fit and there you go, your windows are now wearing a vest. My grandmother will be pleased!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-87180853118002789642011-12-02T05:56:00.000-08:002011-12-02T05:56:27.593-08:00Advent = Carols<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">In my book, Christmas doesn’t really start until Advent, and the first step of that is with me opening my Advent calendar (it was a snowman, in case you’re wondering)! So now that’s over with I can turn my attention to some Christmassy music. I love really Christmassy songs, they fill your heart with the joy of the festive season and make you wish for snow!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">But enough of my Christmas reverie! Today it’s all about how those delightful notes reach your ears. It starts with a vibration. Let’s explore how the note is made by looking at guitar strings.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">There are six strings on a guitar, but they all have the same function. It’s just that the wires are of different thicknesses. When you pluck a string, it vibrates, and the length of the waves that go up and down the strings affects the pitch. Longer waves mean lower notes and shorter waves mean higher notes. Thicker strings are automatically lower because it’s harder to bend them, so the waves are forced to be longer.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQi-Iz2SgAKLqhek8LJluXClGTeBLinoj93iozWybi_9n_TN9n4Eu-EQDotiU6NkOmzikiMCEPdptpEBuAfE2eC4E80IZ_wA3Tv1zoF-InYXesbj3-4QNp1etPkIa-BMSW7jvlevP2P6U/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="290" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQi-Iz2SgAKLqhek8LJluXClGTeBLinoj93iozWybi_9n_TN9n4Eu-EQDotiU6NkOmzikiMCEPdptpEBuAfE2eC4E80IZ_wA3Tv1zoF-InYXesbj3-4QNp1etPkIa-BMSW7jvlevP2P6U/s400/fig1.jpg" width="400" /></a></div></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">From these strings, the waves in the metal push and pull the air around it, turning the physical vibration of the guitar into an invisible vibration in the air – a sound wave.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7s6Wbj-k5mDI1D2S7oe8Ao6njmyqc_pr1jxHMmSzhO3sRLAN24mNwK1PVf-dmrfLK9FxYZjcmrzdZ2QxmpGcQbz0xtIV41oz597pGhdyRvSxgp2vjNcPrl9cJKBU91x81V5F7zV0m9nk/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="290" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7s6Wbj-k5mDI1D2S7oe8Ao6njmyqc_pr1jxHMmSzhO3sRLAN24mNwK1PVf-dmrfLK9FxYZjcmrzdZ2QxmpGcQbz0xtIV41oz597pGhdyRvSxgp2vjNcPrl9cJKBU91x81V5F7zV0m9nk/s400/fig2.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">This sound wave travels through the air by the molecules vibrating those next to each other in turn, until the ones near your ear vibrate your ear drum and you hear the sound.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiDEJxV4AuNfFX8BldND7hKzlrOHD9YCUPMbLMhUFkZTVPcWO4G4HEfouJKFsYaCXwFgIhi5PV0Gzs9_GgX-p9V5yqGAhRRTVShi3IDnpJSA_8Nk-sgbjoiIqQuxTvv2EvZ7XPdoW6E2Y4/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="232" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiDEJxV4AuNfFX8BldND7hKzlrOHD9YCUPMbLMhUFkZTVPcWO4G4HEfouJKFsYaCXwFgIhi5PV0Gzs9_GgX-p9V5yqGAhRRTVShi3IDnpJSA_8Nk-sgbjoiIqQuxTvv2EvZ7XPdoW6E2Y4/s320/fig3.jpg" width="320" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Now obviously, this all happens rather a lot faster than I’ve described – when you’re close to a guitarist you won’t tell any difference between seeing him play and the sound that you hear. But when you’re far away the light from the guitarist reaches you faster than the sound wave, so you see him play the note before you hear it. This is because although the sound waves travel quite quickly, all those vibrations take time to transmit when compared with the speed of light.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">This is why you can tell (approximately) how far away thunderstorms are – as the light (lightning) reaches you much sooner than the sound (thunder)!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-57978843765370327042011-11-24T05:13:00.000-08:002011-11-24T05:13:27.649-08:00And Logic<div class="MsoNormal">Last time we talked logic we looked at switches and the way that input and output were related by the opening and closing of the “gates” – see this <a href="http://getintophysics.blogspot.com/2011/11/simple-logic.html">here</a>. </div><div class="MsoNormal"><br />
</div><div class="MsoNormal">In conventional logic, things are a little more complicated. You can think of a logic gate like a gatekeeper to a fort, where you have to meet the requirements to be allowed to pass. If we take an AND gate, the most simple gate, you can think of it in terms of taking offerings (or bribes, if you want to look at it that way) to the person on the gate. </div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhP76IkcVs3kQNaPFcSmNgQ-0fzSW3WQScSEgEHrdOOYr6y8Row2FY3nEnyTu31R3Q-wIme4RockgpFRaZOrADPE1I15F0qlFlQRmNSwdeKeBa9vf1Y3RkRhhIH-O9BK47qmag9ckTup_k/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="290" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhP76IkcVs3kQNaPFcSmNgQ-0fzSW3WQScSEgEHrdOOYr6y8Row2FY3nEnyTu31R3Q-wIme4RockgpFRaZOrADPE1I15F0qlFlQRmNSwdeKeBa9vf1Y3RkRhhIH-O9BK47qmag9ckTup_k/s400/fig1.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal">If you bring something in your right hand AND something in your left hand, you will be let through by the greedy gatekeeper. And it’s the same with these gates. The only thing is, they don’t accept bribes. But they do love electric current. So a high electric current through both inputs should do the trick.</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh30KY2oI8i-RklCT5tlFL5lLpjTbfhLMZlf5okgH8b5_5dEuc-0hMnaT8kPagZCNhF0i1-rE1Wvn1nQs_o9xqkzBTDl5he4sB66ga304G-KcwhNRhKk7kVz3fKCVfxD47fxroXTGbicZs/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="290" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh30KY2oI8i-RklCT5tlFL5lLpjTbfhLMZlf5okgH8b5_5dEuc-0hMnaT8kPagZCNhF0i1-rE1Wvn1nQs_o9xqkzBTDl5he4sB66ga304G-KcwhNRhKk7kVz3fKCVfxD47fxroXTGbicZs/s400/fig2.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal">So we can again write a truth table, so that we can see the outcomes of all the inputs. Rather than switch on and switch off here, we’ll use low current and high current. Low currents aren’t any good for bribing with, so they are sometimes also denoted with a 0, and high currents with a 1. Outputs can be written in either form as well, but we’ll use high for a successful outcome.</div><div class="MsoNormal"><br />
</div><table cellpadding="5" class="center"><tbody>
<tr><td><b>Input 1</b></td><td><b>Input 2</b></td><td><b>Output</b></td></tr>
<tr><td>low</td><td>low</td><td>low</td></tr>
<tr><td>high</td><td>low</td><td>low</td></tr>
<tr><td>low</td><td>high</td><td>low</td></tr>
<tr><td>high</td><td>high</td><td>high</td></tr>
</tbody></table><br />
<div class="MsoNormal">You might notice that these are the very same outcomes as for the two switches in the circuit we used last time!</div><div class="MsoNormal"></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-57847079946796766002011-11-17T05:10:00.000-08:002011-11-17T05:10:23.910-08:00L<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Yes that’s right! This is my 50th getintophysics blog post! And so to celebrate in true style we will (drumroll please) find the centre of mass of L – fifty in Roman numerals for those at the back.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Centres of mass are important because they help us model things more simply. For example, if we wanted to track a ball through the air, we could easily find the centre of that ball and say that that’s a good approximation of what the ball does. But with shapes that are a bit more complicated, sometimes we want to make things as simple as possible and reduce the object to a single point at the centre.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">But where is the centre of an oddly-shaped item like an L? How do you work out the middle? And what if it’s heavier in one spot than another? That's where the centre of mass comes in.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Let’s start with a simple shape, an equilateral triangle. Using a drawing pin, a string attached to it and a board on the wall, loosely pin the triangle to the board by one of its points. It will hang freely and come to rest. Then use the vertical string as a guide for a ruler to mark a straight line vertically downwards from the pin.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhqOSU20sG6birtIp4w3X1etbDIoJ_SAmUazDPSW6WMYbqnbTl7ifoQRzMmnt2tpMlk_YSzyslc3dFMXheNm8n_8vgA0HfI9zYtbP1y53eEaLB6239Zenl1ekfQl9tgRFrqBPNdIzzSPHI/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="220" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhqOSU20sG6birtIp4w3X1etbDIoJ_SAmUazDPSW6WMYbqnbTl7ifoQRzMmnt2tpMlk_YSzyslc3dFMXheNm8n_8vgA0HfI9zYtbP1y53eEaLB6239Zenl1ekfQl9tgRFrqBPNdIzzSPHI/s400/fig1.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Then repeat with two more points – easy when you have a triangle! So you get a spot where they have all intersected. Congratulations, you have the centre of mass!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjhVCy-ipJM6855gWQscVYcNPdpyxNurAByVp168sHJDAPAwL0Qb3dTEy0KWDT9ZR4N6Sp2O9GOU6smrJ44ZdGrqSdbsgnkGOHxZUKGDjnuBSOuK_kGOWOYE59IPl4AIl1tsA5-ly5IAfY/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="220" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjhVCy-ipJM6855gWQscVYcNPdpyxNurAByVp168sHJDAPAwL0Qb3dTEy0KWDT9ZR4N6Sp2O9GOU6smrJ44ZdGrqSdbsgnkGOHxZUKGDjnuBSOuK_kGOWOYE59IPl4AIl1tsA5-ly5IAfY/s400/fig2.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Doing irregular shapes works in just the same way, choose three points (quite far apart is best) and use the vertical line to create three intersecting lines. It’s often quite surprising where the centre of mass is! You can try this easily at home by taking a piece of paper, cutting a random shape and then use the method.</span><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmu2Hwevij4x4PLfq_iJXzdkS5ZKV8afyOz27ReCPYl_HrgzdwABrK4Y_eZearXYUs0B64qGa7FhpAelkcWI5O_xPEQqp2XUxKRxVOzLoZwT5XnDTpefghhLcpKv313BvAoam-XMitAuc/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="290" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmu2Hwevij4x4PLfq_iJXzdkS5ZKV8afyOz27ReCPYl_HrgzdwABrK4Y_eZearXYUs0B64qGa7FhpAelkcWI5O_xPEQqp2XUxKRxVOzLoZwT5XnDTpefghhLcpKv313BvAoam-XMitAuc/s400/fig3.jpg" width="400" /></a></div></div><div class="MsoNormal"><br />
<span style="font-size: 12pt; line-height: 115%;">It has to be said, for a 50th post celebration, L is quite a tricky letter. I blame the Romans. That’s because once you get started you’ll see that the intersection isn’t actually on the shape itself. But don’t let that stop you. Use tracing paper or something else you can see through, trace the outline of the L on to it. Then when you hang the shape, you can line the tracing paper up and mark the vertical lines on the tracing paper instead.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjh_keinkKlmISAJP1fm04T-ORk8-JduMFOitN90yerBeTogfaxs65oimMDATIGPgODqE_8F0xWkyS21bCzbQ4NWhz5BXWD3UhM1ABH_lYWgytZvPcEsGbIeJMq_9-52LF0EA0raDS3XG0/s1600/fig4.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="290" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjh_keinkKlmISAJP1fm04T-ORk8-JduMFOitN90yerBeTogfaxs65oimMDATIGPgODqE_8F0xWkyS21bCzbQ4NWhz5BXWD3UhM1ABH_lYWgytZvPcEsGbIeJMq_9-52LF0EA0raDS3XG0/s400/fig4.jpg" width="400" /></a></div></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Hurrah! 50 posts and the centre of mass of 50 (in Roman numerals)!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-48099480270342165192011-11-15T05:13:00.000-08:002011-11-15T05:13:54.155-08:00Conducting the Show<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">One of my favourite experiments we ever did in my Physics classes at school was really simple, but also fascinating. I was reminded of it as I hugged my hot water bottle against the cold yesterday! It’s all about the way that heat is transferred through solids, which is called conduction.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">We’ve covered similar topics <a href="http://getintophysics.blogspot.com/2011/06/black-is-new-white.html">here</a> and <a href="http://getintophysics.blogspot.com/2011/08/its-getting-hot-in-here.html">here</a> previously, so I’ll get right down to the experiment itself. To set it up you’ll need at least three bars, of equal diameter (around 0.5-1cm is good) and length but of different materials – like one metal, one wood and one plastic, but more is better, particularly if you can get several types of metal. If you want to try this yourself, why not ask the local hardware store to help, but be careful, this experiment gets hot!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgV0W0BMbSHo_DMut1ZsnFrmseM5nl6KAuSDYzkHslTihg8ko30yOS5v-fBfDhXZGrFSfQajTq5HTaNepvrmWWPHZ8gJEJk_R_JPMlWp5MsI2JDKuhtL_BZKkb640wsquwhae2NFTbNvI8/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="220" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgV0W0BMbSHo_DMut1ZsnFrmseM5nl6KAuSDYzkHslTihg8ko30yOS5v-fBfDhXZGrFSfQajTq5HTaNepvrmWWPHZ8gJEJk_R_JPMlWp5MsI2JDKuhtL_BZKkb640wsquwhae2NFTbNvI8/s400/fig1.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Melt some candle wax and dip one end of each of the bars to the same depth. Leave to cool. Once they are cool you can set them up by a heat source. You could use a radiator or if you’ve got a proper experimental set-up in a lab, a Bunsen burner is normally used as it’s faster. Make sure that all the bars are in a secure position because they will get hot!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3IOV1jW-P1lwEGQVaQUGMnrjd4QELyq5g7KZWlL7fjkYfZF7MRNqTQ_N1KuIMeJuUwvLDo63j8n51a9gIqiGcrgaxdZib5Y41Vrbg1EyR3EtCKl1Efetj1T2ifHGv7H7aq__cryJgE6M/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="220" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3IOV1jW-P1lwEGQVaQUGMnrjd4QELyq5g7KZWlL7fjkYfZF7MRNqTQ_N1KuIMeJuUwvLDo63j8n51a9gIqiGcrgaxdZib5Y41Vrbg1EyR3EtCKl1Efetj1T2ifHGv7H7aq__cryJgE6M/s400/fig2.jpg" width="400" /></a></div><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Then it’s time to get heating. Make sure that the heat is distributed evenly, and put some newspaper down underneath the bars. The molecules inside will start to conduct the heat down the bars, in some much more quickly than the others. Which do you think will lose all its wax first? Think about how free the molecules are to move and transfer their heat to their neighbours!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-22618364413530990062011-11-09T05:19:00.000-08:002011-11-09T05:19:39.358-08:00To Be Precise<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;"> Measuring things is something we come into contact with every day – that bag of apples in the supermarket says it weighs 1.2kg, we give our height in centimetres if we’re young, or feet and inches if we’re less young, and we’ll describe things in terms of London bus units (or at least the news people do). <a href="http://getintophysics.blogspot.com/2011/05/how-do-you-define-kilogram.html">Previously</a>, we’ve looked at our basic units of measure and how they are set in stone so that everybody around the world knows that their 1kg = 1kg somewhere else and so on.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Whenever something is measured, the results are known as data (a plural word, which can get a bit confusing). And these data falls into two categories. If something has a very definite number attached to it, like shoe size, or the number of people on a bus, then this is called discrete data. It means that you can be very sure on the accuracy of your data, because you can’t really have half a person on the bus. Ok, I hear you say, but you can have half shoe sizes. But you can’t have a shoe size of 6.59 or something like that. These are distinct pieces of data.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">The other type of data is called continuous data, and this is the more common form of data. Time, angles, distance, weight and more all fall into this category. And the instruments you use to measure your data, and how accurately you can measure with them will have an effect on your data. Let’s take a simple example. We want to measure our hand span – and there is a choice of three items. One, is a ruler that measures in inches. The second is a ruler that measures in centimetres, and the third is a ruler that measures in millimetres.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQPILbCTH12W0_Hl6xj5REIaFoj1P_q8zjpHg4zydM81yD1XmmvOHqJrQd_D9fWJ-mrvjZpvHcI8PaQv9OlbMCm0U7NCTs_sHwGhRKr8X3SvzJNYcjq08ijmChnQUc9tQXDelc1SSdHBw/s1600/fig+1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="220" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQPILbCTH12W0_Hl6xj5REIaFoj1P_q8zjpHg4zydM81yD1XmmvOHqJrQd_D9fWJ-mrvjZpvHcI8PaQv9OlbMCm0U7NCTs_sHwGhRKr8X3SvzJNYcjq08ijmChnQUc9tQXDelc1SSdHBw/s400/fig+1.jpg" width="400" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">The inch rule has the largest gaps between the markings, so perhaps we can measure to within half an inch of the true size. That means we think the real measurement is, for example, 7.5ins </span><span style="font-size: 12pt; line-height: 115%;">± </span><span style="font-size: 12pt; line-height: 115%;">0.25ins. Similarly, with our centimetre ruler, we can see to the nearest 0.5cm, so we know that the real hand span is 20 </span><span style="font-size: 12pt; line-height: 115%;">± </span><span style="font-size: 12pt; line-height: 115%;">0.25cm. This is slightly more accurate as a centimetre is smaller than an inch. And using our millimetre ruler we can see to the closest millimetre, so we know that the distance we’re measuring in 205 </span><span style="font-size: 12pt; line-height: 115%;">±</span><span style="font-size: 12pt; line-height: 115%;"> 0.5mm. That’s a lot more accurate still.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">There are other, better ways to measure even more accurately with a whole range of specially designed tools which you will learn about during your experiments. But always bear in mind that you are limited by your equipment!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-15347883142055899102011-11-03T06:10:00.000-07:002011-11-03T06:10:49.011-07:00Simple Logic<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Imagine a field, with sheep in. But don’t count them, I don’t want you falling asleep! The field has a fence, and the fence has two gates. If we’re trying to keep the sheep in, we need to make sure that both the gates are closed! Simple.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Now change the field for a circuit that looks like this:</span><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhEzOOIlXXPpsFj7sllDzG6nK7s2fXQPgte-B0iR8Io8pCAc52l5eVvvDPPbUVPcgRwxh3VKSPM5bROiP1-Z-P4RNk_eqASqL3ubYc7Yqul2cRCUgTRacWogTQM5eTMiuIYXb32AAdfLM4/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="236" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhEzOOIlXXPpsFj7sllDzG6nK7s2fXQPgte-B0iR8Io8pCAc52l5eVvvDPPbUVPcgRwxh3VKSPM5bROiP1-Z-P4RNk_eqASqL3ubYc7Yqul2cRCUgTRacWogTQM5eTMiuIYXb32AAdfLM4/s400/fig1.jpg" width="400" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">So, you can see that the sheep, I mean the electrons, can only flow around the circuit (rather than escaping? electrons don’t do that…I see my analogy has fallen apart somewhat) when both gates, or switches, are closed. And when this happens, the light goes on.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">This is the simplest form of logic system, and the different outcomes we can expect are written as a truth table. We can build a system to test this, or just use our brains, because we know that for a current to flow, we need an unbroken circuit.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Truth tables, despite having such a friendly name, can be a little confusing, because instead of using OPEN and CLOSED for the gates, they use 0s and 1s. 0 means that the gate is open, think of it as no electrons getting through. And so 1 means that the gate is closed. When it comes to the output, 0 means NO LIGHT in our bulb, and 1 means LIGHT.</span></div><br />
<table cellpadding="5" class="center"><tbody>
<tr><td><b>Gate A</b></td><td><b>Gate B</b></td><td><b>Output</b></td></tr>
<tr><td>0</td><td>0</td><td>0</td></tr>
<tr><td>1</td><td>0</td><td>0</td></tr>
<tr><td>0</td><td>1</td><td>0</td></tr>
<tr><td>1</td><td>1</td><td>1</td></tr>
</tbody></table><br />
<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">This is the simplest logic gate that you can make, but more complicated gates exist when you want your electronic circuits to work in a more complex way…I’ll be adding another instalment on logic soon!</span></div><div class="MsoNormal"><br />
</div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-314490635408334062011-11-01T06:25:00.000-07:002011-11-01T06:25:48.981-07:00The Might of Hercules<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Looking out across cities under construction today and you’ll see hundreds of huge cranes of all shapes and sizes reaching high into the air and helping builders make ever taller constructions. But these things just didn’t exist in the past, so how did the Romans build their huge buildings, like the Colosseum?</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Manpower, I hear you say! Well, that’s certainly true that they may not have had to pay quite as much per worker as the modern contractors, and slaves were easy to come by, but that’s not quite the answer either.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">They had all sorts of clever contraptions to minimise effort when raising the huge stones, and one of the key concepts is pulleys. Pulleys involve a rotating disc with a free-running rope or wire running around them, and can significantly decrease the amount of work you have to put in to lift something off the ground.</span></div><div class="MsoNormal"><br />
</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhEClDqxQRF4YGtiFFJU5c8PYmoT8UrI_ehGJBWxf_VO_XrvTJL1XeCYIpkIuKkOrQH1TsnD50g4LA0eIv1CrE3mrmlfdduB-PZeQoQpXfzcWA6XInOJ6iWTRHj4rHfPU_ybVOUaEC5oJg/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="236" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhEClDqxQRF4YGtiFFJU5c8PYmoT8UrI_ehGJBWxf_VO_XrvTJL1XeCYIpkIuKkOrQH1TsnD50g4LA0eIv1CrE3mrmlfdduB-PZeQoQpXfzcWA6XInOJ6iWTRHj4rHfPU_ybVOUaEC5oJg/s400/fig1.jpg" width="400" /></a></div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Now, with a simple pulley system, to lift the weight, you have to use the same force as the weight itself. But with more complex systems, you start to only require a fraction of the force you needed before</span></div><div class="MsoNormal"><br />
</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjY_EfcUMb5U1JQ3Kp4ylqlv4N-7lsl0CgX8HWIWUZ5g0PkdPsZS-Oq_Bo8yU4XWt4Pv66Mvj0iYDvB2grEiEoeEfChTQ8xYWixj4OiUhC-Qmu_wguil3YdXj3GzwGDEAxkrAe-1TTanxQ/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="236" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjY_EfcUMb5U1JQ3Kp4ylqlv4N-7lsl0CgX8HWIWUZ5g0PkdPsZS-Oq_Bo8yU4XWt4Pv66Mvj0iYDvB2grEiEoeEfChTQ8xYWixj4OiUhC-Qmu_wguil3YdXj3GzwGDEAxkrAe-1TTanxQ/s400/fig2.jpg" width="400" /></a></div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Here, the force required has dropped to a third of the original weight</span></div><div class="MsoNormal"><br />
</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhqXKeAgGczESzxQL5bG6v8KZnUWWILqedbsffQjkpvROECsH7NnbobuvtrlVFl-YHNVRmGYOJn6Fz174Xb20p-s6SVZxkI2vbdfIOwsgjxbj_g1Fa92A-5xupFt9jusR7cXw8JcqFDrDo/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="236" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhqXKeAgGczESzxQL5bG6v8KZnUWWILqedbsffQjkpvROECsH7NnbobuvtrlVFl-YHNVRmGYOJn6Fz174Xb20p-s6SVZxkI2vbdfIOwsgjxbj_g1Fa92A-5xupFt9jusR7cXw8JcqFDrDo/s400/fig3.jpg" width="400" /></a></div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">And here, it's dropped to a fifth!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">So you can see, that if you can divide the weight of the stone by five, what was one a 500kg block that you would need a LOT of manpower to move, suddenly becomes something that four or five men could wrestle into place. And that makes a big difference when you’re making something that’s so big, it’s still impressive today – even though later inhabitants have been using it as their very own ready-made-bricks store!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">One final note – it’s important to think about the assumptions we’ve made too, and here we’ve neglected any friction in the pulleys. This is probably not an insignificant amount of force, especially if we’re dealing with huge stones, but it’s easier to see the point without such things muddying the waters! </span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-45677604662931340672011-10-27T05:13:00.000-07:002011-10-27T05:13:56.410-07:00One Way Street<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">I’m a fan of walking, but as such that means that I’m very often crossing the road. Now you’d think that the main danger would be cars, but it’s not! It’s bikes. It’s very rare you see a car going down a one way street the wrong way. And if they do, it’s very often with a look of cringing embarrassment with a side of well-I’m-pointing-this-way-now!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Bikes on the other hand are a different matter. They go everywhere, whether it’s the wrong way down a one way street or not, regardless of how many half asleep people there are making their way to work! Now if only there was a better way of making sure that people didn’t do things like that than just putting up signs.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">If only there were diodes for people. Diodes are an important electronic component, and they work by only letting electrons flow through them in one direction, so they are effectively a one way street for electrical current. This means that you have to insert them into your circuit the right way round, otherwise it will never work!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhjSDSpWcfzsL2YlJrD39q2pihbsdOtLL9uSuIHH3HU3GccJ7Ncx-6JAOZk06vAcxq6HA77Jp9n2x7e-9YxEgzIJS-STu77AokE3npuCmgX-Z8y6_dCXsvBim0wtQ_D3nEuqOUpzV8H-dg/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="189" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhjSDSpWcfzsL2YlJrD39q2pihbsdOtLL9uSuIHH3HU3GccJ7Ncx-6JAOZk06vAcxq6HA77Jp9n2x7e-9YxEgzIJS-STu77AokE3npuCmgX-Z8y6_dCXsvBim0wtQ_D3nEuqOUpzV8H-dg/s320/fig1.jpg" width="320" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">You can see from the electrical symbol for the diode which way it works, and when you see a diode, there is a flat side to it that corresponds with the flat side of the triangle, or a direction written on it. Diodes work by having a very low resistance in the correct direction, and a very high <a href="http://getintophysics.blogspot.com/2011/05/resistance-is-futile.html"> resistance</a> in the opposite direction. These days, the type of diode most commonly found is the light-emitting diode, normally shortened to LEDs:</span><br />
</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjZlVHdcWhX5-DIyr3Ns-szf0g3DcL_XBcjz4Uy63wTZOfPRaIGt5rgmiyZCz1NeuOfTFhDBLOyHqVKr94mhPy0fjHgOHAeOZfCDoRKA9Y0cIJemyIH3O0ZIEEeGQBxoSAyEh2jpvae5lA/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="189" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjZlVHdcWhX5-DIyr3Ns-szf0g3DcL_XBcjz4Uy63wTZOfPRaIGt5rgmiyZCz1NeuOfTFhDBLOyHqVKr94mhPy0fjHgOHAeOZfCDoRKA9Y0cIJemyIH3O0ZIEEeGQBxoSAyEh2jpvae5lA/s320/fig2.jpg" width="320" /></a></div></div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Ah, you say, LED TVs are the next big thing! So now you know that inside these new pieces of technology are lots of diodes, whose one-way system I would like to borrow for our streets!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-18180597800282919832011-10-25T05:26:00.000-07:002011-10-25T05:26:45.145-07:00Helpful Decay<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">It seems like every time that radioactivity hits the news it’s a bad story, with nuclear power plants bearing the brunt of the public’s distrust of all things radioactive. But you’ve probably got at least one thing in your house that works by radioactive decay, and there are loads of other useful applications too.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">I wrote before about radioactive decay <a href="http://getintophysics.blogspot.com/2011/04/half-life.html">here</a> but I didn't calrify the three types, alpha, beta and gamma. They are all created by processes which are very similar, just the end product is slightly different. These rays are characterised by how easy it is to stop them. If you think about a light beam, it’s not stopped at all by thin glass, but a really thick piece of glass will make it much dimmer. And it can’t get through walls or anything solid like that.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">These rays are just the same, there are things that they can pass through, and things that stop them. Alpha rays are the weakest, and are stopped by less than a mm of lead, or even a very thick piece of paper. Beta rays need a few cm of lead to stop them and gamma rays need even more. Lead is used as the standard measurement here because it’s a very dense material, offering plenty of bulk to absorb all that radiation.</span></div><div class="MsoNormal"><br />
</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjwl3N_t7qmUUlNqtqSMfcGR9yErY6J1X2vZ9yARPUG_ucGZ0xed8TJ6SQdHNsQBmxAAHIkdZJkGj8YTAHJy5Mx7npg-nn_to05Qg3x2oxgp8XN35mLNDW3XIdnL2NqN6pVNfo_pvDspz4/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="220" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjwl3N_t7qmUUlNqtqSMfcGR9yErY6J1X2vZ9yARPUG_ucGZ0xed8TJ6SQdHNsQBmxAAHIkdZJkGj8YTAHJy5Mx7npg-nn_to05Qg3x2oxgp8XN35mLNDW3XIdnL2NqN6pVNfo_pvDspz4/s400/fig1.jpg" width="400" /> </a></div><div class="separator" style="clear: both; text-align: center;"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;"></span></div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Firstly, this is good to know if you want to be protected from radiation when you’re working in close quarters with a source. But that’s not all it’s useful for.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Alpha radiation, because it’s so easily stopped, is very often used in smoke alarms as the detecting device. This works with an alpha-source on one side of an air gap and a detector on the other. In normal use, the radiation reaches the detector just fine. But if the air gap fills up with smoke particles, this is enough to stop the rays, and the alarm sounds.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEga3jG6kBXmYC_JGX1M07HiT1rSloJ5o-LEXbLQBoxF25vXG4t5DH5u0u-mT_xoq14Pe4S0Nn_pGG-u23oeUOylRwmCbMWHXcCQmjx_0VqVNXjISnrzDzv6xDom9YAhjauKTGl2cX1X0g4/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="220" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEga3jG6kBXmYC_JGX1M07HiT1rSloJ5o-LEXbLQBoxF25vXG4t5DH5u0u-mT_xoq14Pe4S0Nn_pGG-u23oeUOylRwmCbMWHXcCQmjx_0VqVNXjISnrzDzv6xDom9YAhjauKTGl2cX1X0g4/s400/fig2.jpg" width="400" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Beta radiation is more commonly used for testing the thickness of things during manufacturing processes. The source is placed one side of the product and the detector on the other. If it gets too thin then too much radiation will get through, and if it gets too thick then not enough will get through. The manufacturing line can then be adjusted accordingly either way.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmIfrSDmZ-Dh5_bzysJQL2_CYUhFSvAm-tWdivY8JtNyOECvwRxO_4vE6qfzzsUyJBH8BYs2w2mDv-eM09PyZQkkM_l5lFs4atryVuFLu4SlNWww57jVzNpTkCUP9tFg9hhMQRVwpDWkg/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="236" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmIfrSDmZ-Dh5_bzysJQL2_CYUhFSvAm-tWdivY8JtNyOECvwRxO_4vE6qfzzsUyJBH8BYs2w2mDv-eM09PyZQkkM_l5lFs4atryVuFLu4SlNWww57jVzNpTkCUP9tFg9hhMQRVwpDWkg/s400/fig3.jpg" width="400" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">So, whilst we can easily be led to believe by the news that radiation is bad, in fact it can be quite useful! It’s just a matter of treating it with respect and making sure that nuclear waste is very carefully looked after!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-67906914897486984282011-10-21T05:39:00.000-07:002011-10-21T06:21:57.807-07:00Compare the Meerkat<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Those comparison websites are everywhere these days, with varying degrees of annoyingness I have to say. But when it comes to comparing electricity prices, or working out the amount your appliances use it’s pretty simple to do the calculations yourself, you just need a few tools to decode the information you’ll get from the companies.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">We’ve previously come across energy being measured in Joules (J) but those canny electricity providers give their prices for kWh, that is, the price for an hour of electricity if you use 1000 Watts. It’s simple to convert Joules to kWh though using the simple equation:</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Energy (in kWh) = power (in watts) x time (in seconds)</span></div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">1 kWh = 1000 x (60 x 60)</span></div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;"> = 3 600 000J</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Now where it gets tricky are all those crazy numbers and dials on the electricity meter, so it’s usually best to wait for a bill to arrive to get all the details off that. On there you'll find a current meter reading, a previous reading, the units used, plus the cost per unit. Nowadays when it’s all worked out you’ll also have a nice huge cost amount as well!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEixan9G9Oo8FnLHc5Qa2_KV_6t3oIFVThHnBk09VUi6CelWmpw2P5NNCUXQfgKP9qwXi4n22LG1hQhcjdRVzlFftAIGuN9yUyHSn8zasrc3pqz2NARu2BIlAwNioPmU6ngo_eXgYQv54V4/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="306" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEixan9G9Oo8FnLHc5Qa2_KV_6t3oIFVThHnBk09VUi6CelWmpw2P5NNCUXQfgKP9qwXi4n22LG1hQhcjdRVzlFftAIGuN9yUyHSn8zasrc3pqz2NARu2BIlAwNioPmU6ngo_eXgYQv54V4/s400/fig1.jpg" width="400" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">So, it’s simple to work out the price once you’ve got all the details:</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjzEGhNT_A_j2HI7L1NwJUurrhWjQMFyE-zyB7gc9wenIvWumxDxThXjs6RWoCAL38AmNahfoVqroI024Vn3d0cypCmCLqVyeLbsDbrmuxvJjdnHtXThvqkPHtelVHC36cDqT8P8-xhqZQ/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjzEGhNT_A_j2HI7L1NwJUurrhWjQMFyE-zyB7gc9wenIvWumxDxThXjs6RWoCAL38AmNahfoVqroI024Vn3d0cypCmCLqVyeLbsDbrmuxvJjdnHtXThvqkPHtelVHC36cDqT8P8-xhqZQ/s400/fig2.jpg" width="400" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Now let’s see how much it costs to run a lamp for 15 minutes. If you want to work this out for one of your items, have a look round it and check out the label. There should the a value on it in watts (W).</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj5ad5MVh44mspvDWHKgBTyzivywHpKT2xhivyLxDR_R8YiRUd77Xe2RTUzgF_BukQ4zeFpnHteVpoT5lbQpEDX2bgA5o-I5VkU8BkLjDNO3ii0L4CdKBykpxefokHkmbb8OBfDVECmW-o/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj5ad5MVh44mspvDWHKgBTyzivywHpKT2xhivyLxDR_R8YiRUd77Xe2RTUzgF_BukQ4zeFpnHteVpoT5lbQpEDX2bgA5o-I5VkU8BkLjDNO3ii0L4CdKBykpxefokHkmbb8OBfDVECmW-o/s400/fig3.jpg" width="387" /></a></div><div class="separator" style="clear: both; text-align: center;"></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">So now you have it, you’re as good as a price comparison site, if not better, since you can work out how much it costs to use any of your appliances in your own house! Well done little meerkat.</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-10180058681035969852011-10-18T05:20:00.000-07:002011-10-18T05:20:43.657-07:00The Sea Breeze<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Ok, so it’s a little late in the year to be going to the beach but I just can’t resist the salty charms of the seaside! I love feeling the sand between my toes, hearing the gentle crashing of the waves and feeling the wind in my hair. Well, actually most of the time the wind is really unnecessary. It’s not like we very often get to sunbathe and it gets so hot we’re glad for a breeze. But that doesn’t matter to the weather!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">It’s always windy at the beach, even when it’s quite calm inland, because of the way that air moves when it gets hot. In the daytime the sun heats the land up faster than it heats the water up. This in turn heats the air above the land. Hot air is lighter than colder air since the molecules are moving faster, making it less dense, so it rises. Cold air from out to sea then rushes in to fill this gap.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhTYLN0nWyPCQOj1IBD0e09XRP5yyPvacN4t74oLqKTKWLbOR0Jl_0lrXYZE-UkYvzauj6nrjpc0vk16FeSXfVlrKyevXioRVMHAgKIktTiSUtNmWgE8_oCeVugBf5knkLh3zXbU7ls-hg/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="291" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhTYLN0nWyPCQOj1IBD0e09XRP5yyPvacN4t74oLqKTKWLbOR0Jl_0lrXYZE-UkYvzauj6nrjpc0vk16FeSXfVlrKyevXioRVMHAgKIktTiSUtNmWgE8_oCeVugBf5knkLh3zXbU7ls-hg/s400/fig1.jpg" width="400" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">As evening falls and the sun starts to lose its heat, the opposite happens. The land cools down a lot faster than the water, so now it’s the warm air out to sea that rises. This creates a breeze in the other direction.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjeDdssU3UW_3mf3dL-A_fTn9nUEGZRu0UoYdETQMvBuPFmMzxQgw9bzMNSeLx70mjg2fEKksK9HmbxEryqh6cJJcHMnKxiDgE1V_lj48LSweEaJmEL5bJXGyV7uwrW2K5Mx2mVZL0k3FI/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="291" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjeDdssU3UW_3mf3dL-A_fTn9nUEGZRu0UoYdETQMvBuPFmMzxQgw9bzMNSeLx70mjg2fEKksK9HmbxEryqh6cJJcHMnKxiDgE1V_lj48LSweEaJmEL5bJXGyV7uwrW2K5Mx2mVZL0k3FI/s400/fig2.jpg" width="400" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">This is an example of convection, which is the way that hot areas of gases and liquids move around. This all happens because of a change in density as the molecules get warmer, as well as the need to keep the space all filled up – there can’t be any unfilled space!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj_FvYq9ZvJFVUYg0BcRr8Zj1HNYYG3AdqdcMrbaZ9MlFGNffp8q2AbbTmU-040tKST6ACPEmq749xFsR_v1T0R0_qVVWI-cyp1_AhoxkvI9jW9oUE-NjThotjSzJ5CO6Y1d3YY6EVbqDI/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj_FvYq9ZvJFVUYg0BcRr8Zj1HNYYG3AdqdcMrbaZ9MlFGNffp8q2AbbTmU-040tKST6ACPEmq749xFsR_v1T0R0_qVVWI-cyp1_AhoxkvI9jW9oUE-NjThotjSzJ5CO6Y1d3YY6EVbqDI/s400/fig3.jpg" width="362" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com2tag:blogger.com,1999:blog-8670065749761940187.post-45395582113519355222011-10-13T05:30:00.000-07:002011-10-13T05:30:00.015-07:00Mirror Mirror On The Wall<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">We take it for granted that the mirrors in front of us show us a true reflection of the world, but it’s not always the case. Like in the funfair’s hall of mirrors, just a small deviation from a true and flat surface can squish, stretch or otherwise change the appearance of the reflected object. But thankfully in Physics we like to assume that our mirrors are always perfectly flat. That is to say we think about the fact that they might not be, but then to simplify our own lives we’ve decided to assume they are.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">As an aside, an assumption is not the same as neglecting to think about certain aspects of your experiment that may have an effect. It’s merely a way of simplifying complicated things, based on deciding to ignore, temporarily, the effect of something. Always state your assumptions, so that you can justify them, or go back and revisit them easily.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">But back to mirrors, now we have a perfectly flat one in front of us, what can we see? Our own faces and the objects around us are crystal clear, only in reverse, but how far away are the things we can see? Are they true to the world around you, or just a projection, like a TV screen?</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhD9M3sJcH5uVG7XDQsXZh656SL97y2J6CFb-qPFF6wRO7PvYjxd5OE5t63X29igSZwAGj6-FO2XKbJwghwaXZSFrBJEjvu1l6eJQnSxeLmH6yX3GKPOuWElzoN0P-5epB4ec4lSLxsIco/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="291" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhD9M3sJcH5uVG7XDQsXZh656SL97y2J6CFb-qPFF6wRO7PvYjxd5OE5t63X29igSZwAGj6-FO2XKbJwghwaXZSFrBJEjvu1l6eJQnSxeLmH6yX3GKPOuWElzoN0P-5epB4ec4lSLxsIco/s400/fig1.jpg" width="400" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">If we imagine looking at a mirror more from the side we can perform a simple experiment to see what happens.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjk2tebs8wbVjo82pHuTR46InkZJwb9NSEyO5v88_VQGnjy3RyVIAguH1MfnEHMsLAWv0rjsVlr-lKh7PbSiTy96AH_WKnoDiU0eBybRPTcglrH0M3PKKTn49nk48C56ralrOkpLvfZPt0/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="291" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjk2tebs8wbVjo82pHuTR46InkZJwb9NSEyO5v88_VQGnjy3RyVIAguH1MfnEHMsLAWv0rjsVlr-lKh7PbSiTy96AH_WKnoDiU0eBybRPTcglrH0M3PKKTn49nk48C56ralrOkpLvfZPt0/s400/fig2.jpg" width="400" /></a></div></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">So the real object and its virtual image appear identical, and as far away from the mirror as each other. This is because the angle of incidence (incoming ray) and the angle of reflection (reflected ray) are always the same with a pure and flat surface. The object distance u is therefore equal to the image distance v. There are loads of ways to test this our yourself, so why not have a go?</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-50938587975205683712011-10-06T05:28:00.000-07:002011-10-06T05:28:32.716-07:00A Perfect Copy<div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"></div><span style="font-size: 12pt; line-height: 115%;">Photocopiers are a bit of a mystery aren’t they? A big, hot box with flashing lights and whirring noises that can churn out copies of your document almost faster than you can blink! But how does it work? Well, we’re back to that old favourite, electricity again!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">It’s all about static electricity once more, which is the small charge which can make balloons stick to the wall (or cats) and can even make your hair stand on end! It’s easy to create a static charge on plastic items like rulers, and if you’ve ever felt a spark from a metal object that’s thanks to static too.</span></div><div class="MsoNormal"><br />
<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhiUMmrQBo6dDry65gEy2mablVkYDlYCklynkDblQa1J985uqPR6ddbiC5_DmfIjQTqpqg3ojnaVNf6DjO9F7NT7CpFAVJeotA3xuhwYV9hOoUEgCSxZnfKDuK1Y9lF2CueO7qoFI7TLUo/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhiUMmrQBo6dDry65gEy2mablVkYDlYCklynkDblQa1J985uqPR6ddbiC5_DmfIjQTqpqg3ojnaVNf6DjO9F7NT7CpFAVJeotA3xuhwYV9hOoUEgCSxZnfKDuK1Y9lF2CueO7qoFI7TLUo/s400/fig1.jpg" width="400" /></a></div><br />
</div><br />
<div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">Sometimes these charged objects are fun, but they can also be hazardous too, like if you were to experience a spark from a static charge when you were near to fuel, for example. This could get very explosive very fast. But it can also be useful and in this case, it’s vital to making copies – fast. Let’s lift the lid and see what happens inside.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">A plate inside the photocopier is negatively charged all over, and this is the centre of the copying system. That bright light you see when the copier makes the copy is because the machine relies on a projection of the image you’re copying. And that image gets projected onto the charged plate. It’s made of a special kind of material so that the light areas lose their charge, but the dark areas keep it.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgkwRVHFEbel0KFWc3H2Sice-HfW29bWnX34XpBJ_GMB0Vn3vz7Zmux8pn5cPDLAdmZUt5hpuzmx1PiW401XPua3vPL4-frtWWgqmFU55hlrWLNJWH-4gZ0PwmSBSXoG-Et4vCXHEMGmtI/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="305" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgkwRVHFEbel0KFWc3H2Sice-HfW29bWnX34XpBJ_GMB0Vn3vz7Zmux8pn5cPDLAdmZUt5hpuzmx1PiW401XPua3vPL4-frtWWgqmFU55hlrWLNJWH-4gZ0PwmSBSXoG-Et4vCXHEMGmtI/s400/fig2.jpg" width="400" /></a></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">The powdered ink (toner) is then applied to the plate, and it sticks to the negatively charged bits, where the dark on the image is. A piece of paper is then pressed onto the plate. It’s heated so that the powdered ink melts and sticks to the paper.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjURw7Qh60ArdsQX7uK6xfzcenUFaiJ__HvzDXLTgMKsOj7kmvJ5y8msbuQ1CPoY4lSYSSK1vbgkFQ8HqQ3JJMPP47p_M8eH_LQBkW8kn-qKFMjj9XJ_5CStsUFq1GAiOy-euIfCTxW0G0/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="291" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjURw7Qh60ArdsQX7uK6xfzcenUFaiJ__HvzDXLTgMKsOj7kmvJ5y8msbuQ1CPoY4lSYSSK1vbgkFQ8HqQ3JJMPP47p_M8eH_LQBkW8kn-qKFMjj9XJ_5CStsUFq1GAiOy-euIfCTxW0G0/s400/fig3.jpg" width="400" /></a></div><div class="separator" style="clear: both; text-align: center;"></div><span style="font-size: 12pt; line-height: 115%;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">All of this happens in super quick time, so it seems incredible that so many processes are involved! And it’s all thanks to the humble electric charge.</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-51783846485426230892011-10-04T05:55:00.000-07:002011-10-04T05:55:32.579-07:00Testing Testing 1....2....3<!--[if gte mso 9]><xml> <o:OfficeDocumentSettings> <o:AllowPNG/> </o:OfficeDocumentSettings> </xml><![endif]--><!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:TrackMoves/> <w:TrackFormatting/> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:DoNotPromoteQF/> <w:LidThemeOther>EN-GB</w:LidThemeOther> <w:LidThemeAsian>X-NONE</w:LidThemeAsian> <w:LidThemeComplexScript>X-NONE</w:LidThemeComplexScript> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> <w:SplitPgBreakAndParaMark/> <w:EnableOpenTypeKerning/> <w:DontFlipMirrorIndents/> <w:OverrideTableStyleHps/> </w:Compatibility> <m:mathPr> <m:mathFont m:val="Cambria Math"/> <m:brkBin m:val="before"/> <m:brkBinSub m:val="--"/> <m:smallFrac m:val="off"/> <m:dispDef/> <m:lMargin m:val="0"/> <m:rMargin m:val="0"/> <m:defJc m:val="centerGroup"/> <m:wrapIndent m:val="1440"/> <m:intLim m:val="subSup"/> <m:naryLim m:val="undOvr"/> </m:mathPr></w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" DefUnhideWhenUsed="true"
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<div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">In the past, when things like huge steel bridges were the latest technology, sometimes they wouldn’t quite work how they were meant to. Every now and then it was a disaster. It was a puzzle for engineers, who were trying their best to make things safe. One man decided to make a difference, a Scot called Kirkaldy. </span></div><div class="MsoNormal"><br />
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</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">He built the world’s first testing machine that could be used to create like-real-life testing situations on large bits of the construction materials. And on Sunday I went to the museum where it’s kept. The Kirkaldy Testing Museum is a small and unassuming place, remarkable only if you happen to notice the “Facts not Opinions” motto above the door.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">By all accounts, he was a rather opinionated guy, with everything he said (well, relating to testing of these large building parts anyway) meticulously based on the results of his tests, which he wrote down in a huge leger so he could check back and show people how right he was. He even kept all the pieces he’d tested to destruction until the sheer weight was in danger of bringing down the building!</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">The tests he carried out were of two types, one a test to stretch the item (tensile test) and another to squash the item (compressive test). These are the two main types of forces that area on major beams in construction, particularly in bridge building:</span></div><div class="MsoNormal"><br />
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</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">The clever part was, that although he could only make his machine go one way, as it was all about water pressure, he managed to both push and pull the samples. He did this with an ingenious method, adding an extra “space” for testing the items in compression (red), the other side of the stretching part (blue).</span></div><div class="MsoNormal"><br />
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</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">For a time, Kirkaldy was the go-to man for any sort of material testing, with his all-singing all-dancing machine the star of the show. It was important to test whole girders, or whole joists, because you couldn’t be sure of the material quality, because manufacturing methods for making the metals were poor. But as these improved, tests could be done on smaller and smaller samples, making this beast obsolete.</span></div><div class="MsoNormal"><br />
</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjEe0yBtzxjXnpCxaY5KxYzaYjj3Wn-kQy1F1S4w0Rd3k6bKTzbHEXZ-I4Wj79uyoG5JQ9m6c738q2LKPQJSiBwU8fiz7QRfDwBwr7DDlLUF19fCdZo9I5dJTj1qn57k5EZVFviiTJdp-c/s1600/fig4.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjEe0yBtzxjXnpCxaY5KxYzaYjj3Wn-kQy1F1S4w0Rd3k6bKTzbHEXZ-I4Wj79uyoG5JQ9m6c738q2LKPQJSiBwU8fiz7QRfDwBwr7DDlLUF19fCdZo9I5dJTj1qn57k5EZVFviiTJdp-c/s400/fig4.jpg" width="400" /></a></div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;"><br />
</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">The museum has a great collection of such testing rigs that are smaller and more compact, for testing littler samples. And today we have electronic machines, capable of getting results so accurate Kirkaldy himself may have had to concede defeat. But none are quite as important as that gigantic pioneering machine!</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-51107270785179493372011-09-30T05:22:00.000-07:002011-09-30T05:22:45.790-07:00Experiments!<!--[if gte mso 9]><xml> <o:OfficeDocumentSettings> <o:AllowPNG/> </o:OfficeDocumentSettings> </xml><![endif]--><!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:TrackMoves/> <w:TrackFormatting/> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:DoNotPromoteQF/> <w:LidThemeOther>EN-GB</w:LidThemeOther> <w:LidThemeAsian>X-NONE</w:LidThemeAsian> <w:LidThemeComplexScript>X-NONE</w:LidThemeComplexScript> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> <w:SplitPgBreakAndParaMark/> <w:EnableOpenTypeKerning/> <w:DontFlipMirrorIndents/> <w:OverrideTableStyleHps/> </w:Compatibility> <m:mathPr> <m:mathFont m:val="Cambria Math"/> <m:brkBin m:val="before"/> <m:brkBinSub m:val="--"/> <m:smallFrac m:val="off"/> <m:dispDef/> <m:lMargin m:val="0"/> <m:rMargin m:val="0"/> <m:defJc m:val="centerGroup"/> <m:wrapIndent m:val="1440"/> <m:intLim m:val="subSup"/> <m:naryLim m:val="undOvr"/> </m:mathPr></w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" DefUnhideWhenUsed="true"
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<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhBTC3gQgSMj62K0WfjQ3zGtIh09lw_DokkLLhnUAQOwB7NqEEkl_smCXj75pWDVQ4JM6WIwDFtx-n_hHeHGnRX5hjzAVqlaUr5x2rTJnbyZ5GHm6aIrfHVh_r7kqFXiysDOIkIVWQxmQ4/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="246" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhBTC3gQgSMj62K0WfjQ3zGtIh09lw_DokkLLhnUAQOwB7NqEEkl_smCXj75pWDVQ4JM6WIwDFtx-n_hHeHGnRX5hjzAVqlaUr5x2rTJnbyZ5GHm6aIrfHVh_r7kqFXiysDOIkIVWQxmQ4/s400/fig2.jpg" width="400" /></a></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12pt; line-height: 115%;">It’s a new school year so it’s time to forget that hesitant you of the past and forge ahead when it comes to taking part in the experiments! It’s much more fun to join in, plus you get first-hand knowledge of the instruments and a better understanding of the point of the task.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">Some of the instruments can be daunting at first, with different scales and lots of confusing numbers, but nobody knows how to read them when they start out! Take a deep breath, look closely and read twice. Get someone else to do the same and compare your answers. Be sure to ask for help if you’re unsure because you can’t get accurate conclusions if you don’t have accurate results.</span></div><div class="MsoNormal"><br />
</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiG5nIJ7W0IvuQbZA750i2LQ6O0whAe_ylyWe3p99hRqWABjYR0h-C_D3boRCj1tqPNWIH5hVej3PYc_Ky5RusqFKvnQLQ4N-fI0XeQC2ERYGJBWde3asi4H0cuNhFRm8XjigE4s7t966U/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="246" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiG5nIJ7W0IvuQbZA750i2LQ6O0whAe_ylyWe3p99hRqWABjYR0h-C_D3boRCj1tqPNWIH5hVej3PYc_Ky5RusqFKvnQLQ4N-fI0XeQC2ERYGJBWde3asi4H0cuNhFRm8XjigE4s7t966U/s400/fig1.jpg" width="400" /></a></div><div class="MsoNormal"><br />
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</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">Always try your best to do the experiment according to the method, as you can be sure that there’s a good reason for doing it that way! If you’re worried that you’re not doing it right, do it a couple of times and record all your results so you can see if it’s repeatable, or if you’re doing something a bit erm, unconventional.</span></div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><span style="font-size: 12.0pt; line-height: 115%; mso-bidi-font-size: 11.0pt;">And keep a neat record of the readings and observations. It’s important to draw up a good table, or somewhere organised to put the results of your experiments. Label things well, include units and note each experiment you do separately. You’re unlikely to get things mixed up if you only do one experiment a lesson, but starting off with the right habits is a great way to keep on top of things.</span></div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0tag:blogger.com,1999:blog-8670065749761940187.post-5386868918136900352011-09-28T05:31:00.000-07:002011-09-28T05:31:12.953-07:00A Fair Exchange Is No Robbery<div class="MsoNormal">In today’s world where electricity can be had at the flick of a switch or the push of a button it’s all too easy to ignore how it gets made, and that for the most part in the UK, we use fossil fuels to produce it. How we convert coal into something that can be used without any fuss, mess, or heat is pretty much a mystery to the general public, but never fear, I’m here to help you answer your burning questions (groan) on getting power from that black stuff.</div><div class="MsoNormal"><br />
</div><div class="MsoNormal">It all starts with the raw materials, coal in this case, being burned in a huge oven. The heat is the useful part, and this is used to heat up water via a heat exchanger. This involves pumping water through a series of pipes that come into contact with the heat. The larger the surface area the better the heat exchange will be.</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjZxFCKGPEVPGJ1zT31yj4dS4kxmolfMV-DG3Dt7iHw13Oex8N6233b5DOnVjDutqGCRql4rEdriTqEv2IGFUqGKDZojwmNYC0kX0XnKAbXLDExggyI9VaqTrL8cgwE1Y62bZwE4mXTFBs/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="260" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjZxFCKGPEVPGJ1zT31yj4dS4kxmolfMV-DG3Dt7iHw13Oex8N6233b5DOnVjDutqGCRql4rEdriTqEv2IGFUqGKDZojwmNYC0kX0XnKAbXLDExggyI9VaqTrL8cgwE1Y62bZwE4mXTFBs/s400/fig1.jpg" width="400" /></a></div><br />
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</div><div class="MsoNormal">This creates high pressure steam from the cold water and this is what is needed to drive the turbines, much like trains used to be powered by steam before the petrol engine was invented. The steam is forced through the turbines, which makes them spin. This spin can then be used to create electrical power through the <a href="http://getintophysics.blogspot.com/2011/05/answers-are-at-your-fingertips.html">dynamo</a> effect.</div><div class="MsoNormal"><br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiC-vCmW4KGFCkN17pg21M23ew3BL1UZOXhBiGTeLCkrjJIuA2qyJnxwcxDcj3SWT8dkytNhI_fLJ-Gpt0jXG9Og_F47XqJaNDV8ZHKe8BJvJ03D7iTBgjqPP31YdPRdbeZJHsLQCoLLAw/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="307" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiC-vCmW4KGFCkN17pg21M23ew3BL1UZOXhBiGTeLCkrjJIuA2qyJnxwcxDcj3SWT8dkytNhI_fLJ-Gpt0jXG9Og_F47XqJaNDV8ZHKe8BJvJ03D7iTBgjqPP31YdPRdbeZJHsLQCoLLAw/s400/fig2.jpg" width="400" /></a></div><br />
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</div><div class="MsoNormal">The electrical power then goes directly into the National Grid, from where it goes to anything that needs it. Seems like a simple enough process but let’s just look at the drawbacks too. Firstly, this relies on fossil fuels, which are becoming more scarce, and secondly, there are a lot of energy exchange processes going on here.<br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidqxwqZ63Ls9RsvTIyXQzcIuCtGMV7MZeqRnlWmeSpzQhQXrNiEs6dH6mvj8oR3lDqjD3mmnqIHZZtvkWKNMqJRa1g2SDtlpHYc3zpkTsCphJ6Xpg8nU9tGuX8Ndt2CRQwVrjAU063IYo/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="155" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidqxwqZ63Ls9RsvTIyXQzcIuCtGMV7MZeqRnlWmeSpzQhQXrNiEs6dH6mvj8oR3lDqjD3mmnqIHZZtvkWKNMqJRa1g2SDtlpHYc3zpkTsCphJ6Xpg8nU9tGuX8Ndt2CRQwVrjAU063IYo/s400/fig3.jpg" width="400" /></a></div><br />
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</div><div class="MsoNormal">The problem with energy exchange is that it’s never a perfect swap, some of the energy is always lost as heat, light or sound and here is no exception. This process is a very hot one, so heat is the biggest way this process loses energy, with some to light as well. The more steps the worse the loss is. Let’s imagine each phase is 70% efficient, and see how much energy we come out with at the other end.<br />
</div><div class="MsoNormal"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEievFv-zQQnoAYQiPBqbCgOt1zMYvHYSV6gd4t9w8XzuH1XeoqzRZJRS16dqsRdLJusKsMeWnYr25vNX5oqr1Sj1pXly3sSR37_zYOUK2DDul3l_q_OGfzLVYKICdebJFlNLabIy7w93_o/s1600/fig4.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="156" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEievFv-zQQnoAYQiPBqbCgOt1zMYvHYSV6gd4t9w8XzuH1XeoqzRZJRS16dqsRdLJusKsMeWnYr25vNX5oqr1Sj1pXly3sSR37_zYOUK2DDul3l_q_OGfzLVYKICdebJFlNLabIy7w93_o/s400/fig4.jpg" width="400" /></a></div><br />
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</div><div class="MsoNormal">So in this example, only 35% of the energy in coal actually goes to making electricity. Whilst this amount is quite shocking, it’s not too far from the mark in some cases, like really old power stations. Newer versions are slightly more efficient, but surely one way to protect our natural resources would be to really maximise the energy that we do get?</div>Dr Emmahttp://www.blogger.com/profile/14273594437920056178noreply@blogger.com0