Outcomes
Students experiment to find the way to make a cork float upright.

Materials
Each student should have a champagne bottle cork, a toothpick and a piece of plasticine.

Procedure
Demonstrate that the corks float. Ask the question, "Can you make your cork float so that Shirley's face is out of the water?" You can use the toothpick and plasticine to help make the cork float upright.

Background
Cork is less dense than water and so it floats when placed in water. We say that the cork displaces more water than it weighs. To make the cork float upright, we need to lower its centre of mass and we do this by inserting the toothpick and plasticine as shown in the diagram. Having the plasticine below the water stabilises the cork, in much the same way that the keel on a yacht helps to stabilise it when being blown by the wind.