Physics can be difficult to learn, but this blog aims to help you get into physics by connecting your GCSE physics lessons with things you see in the world around you.

## Friday, 2 December 2011

### 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)!