Archimedes Challenge

A pretend stone wall in the background with a scale and wheel sitting on a brown table in the forground surround by a clear perspex box.
A pretend stone wall in the background with a scale and wheel sitting on a brown table in the forground surround by a clear perspex box. To the right on the wall is a blue information panel titled 'Archimedes Challenge'.

When an item is placed into water, the volume of water it shifts or displaces can be used to calculate the item's density (and value).

How it works

Lower a balance containing a crown and a 'gold' bar into water and discover they are unbalanced due to their different densities.

Things to try or ask around the exhibit

  • Is this crown made of pure gold?
  • Why does the crown and gold bar appear to be equally balanced (and equal mass) in mid-air, but unbalanced underwater?

Background

When measured on the scales in mid-air, the crown and the gold bar show equal mass on the scales. When they are lowered together into the water, one of the items is indicated as being heavier on the scale.

This is because the gold bar and the crown are the same mass, but they each have different densities. One is more dense than water and one is less dense than water. An object's density is measured by dividing its mass by its volume.

Finding the science in your world

The mathematician Archimedes iscovered principles about buoyancy while he was having a bath. He was so excited that he jumped out of the bath and ran around town naked, shouting “Eureka!”