## About this blog

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.

## Thursday, 8 December 2011

### 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!