Saturday, September 10, 2011

There’s Something in the Water

We are massive fans of Opua School in Northland.  Last time we were there we saw them braving the weather and floating their own rafts.  Their efforts inspired this blog which is all about why some things float and others sink. 

You will need:
  •  A large sheet of tinfoil
  • A jug or large transparent container of water
  1. Fold the sheet into a boat (like in the photo)
  2. Place it on top of the water
  3. Now, screw your boat into a ball
  4. Try floating that!
Unfortunately, it’s not as easy as “light things float and heavy things sink”.  Luckily for us, Archimedes had the famous Eureka! moment and figured it out.  He noticed what happened to the water level when he got in the bath. 

Push you hand in the jug of water. What happens to the water level?

What we need to know:

The tinfoil applies a downward force on the water. But the water has an upward force on the tinfoil.

The two bits of information we need to look at is the amount of water we displace (move) and the weight of that displaced water and compare this to the weight of the tinfoil.

When the tinfoil is lighter than the water it pushes out of the way - it floats.
When the tinfoil is heaver than the water it pushes out of the way - it sinks.

Our tinfoil boat pushes more water out of the way than our tinfoil ball – the boat floats but the ball sinks.

Hope you enjoyed this blog and to inspire you to get creative with science – check out the hardy souls of Opua School putting floating and sinking into action.

Remember – keep safe -