Toys and Physics - Heat energy

3.1 Galileo thermometer

What happens
The sphere rise and fall as the temperature falls and rises. More of the glass spheres are at the bottom when the temperature is high.

Theory and teaching notes
The density of the liquid varies with temperature and so the level at which each carefully weighted ball floats will also change. They will float at the same level as their average density.

3.2 Heat sensitive animals

What happens
The animals change colour when immersed in hot water.
You can also buy mugs where the design on the outside changes when they are filled with hot liquid – some interesting effects can be produced!

Theory and teaching notes
Parts of the animals are made of heat sensitive plastic.

3.3 Heat sensitive mat

What happens
The mat changes colour when you put your hand on it or when a cup of hot drink is placed on it. The colour depends on the temperature of the object.

Theory and teaching notes
The crystals are heat sensitive and change colour as the temperature rises or falls.

3.4 Heat sensitive Red noses

What happens
As the red nose is warmed it changes colour. Some noses turn pink, others turn yellow.

Theory and teaching notes
The noses are made of a plastic that changes colour when heated. You could investigate the temperature needed for a colour change to occur.

3.5 Holly's Passion pen

What happens
When you hold the base of the pen liquid bubbles up into the bulb.

Theory and teaching notes
The liquid is very volatile and the heat energy from your hand is sufficient to evaporate it forcing liquid up the stem of the pen into the bulb at the top. The hotter your hand the more liquid evaporates.

3.6 Heart warmer

What happens
The heart gives out heat and can be used to keep you warm.

Theory and teaching notes
The heat can be 'regenerated' by putting it in hot water. As it cools it gives out heat.

3.7 Radiometer

What happens
When heat radiation falls on the vanes they spin round.

Theory and teaching notes
This is an excellent piece of apparatus for demonstrating that dull black surfaces absorb heat radiation better than shiny ones. The glass bulb is filled with low pressure air and as radiation falls on the vanes the black surfaces absorb more radiation than the silvered ones, the air near them heats up - expands and so pushes the vanes round.
Try placing a sheet of glass or a beaker of water between the heat source (a small electric fire, candle, light bulb or bunsen burner) and the radiometer and investigate the effect of these materials on the transmitted infrared radiation.