Eureka!

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.

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!

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.

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.

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.

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!

Wear A Vest!

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!

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!

As we learned before here 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!

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.

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!

Advent = Carols

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!

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.

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.

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.

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.

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.

This is why you can tell (approximately) how far away thunderstorms are – as the light (lightning) reaches you much sooner than the sound (thunder)!