You will need: different foods - cling film or metal foil - a stopwatch

Wrap up a piece of chocolate. Hold it in your hand for two minutes.
What do you notice?
Does it make a difference if you hold it for longer?
Try this with other foods.
Compare what happens with the foods. Is there a pattern?

When a candle burns, the hot flame begins to melt the wax.

You can also cool materials.
A liquid will change to a solid if it is cooled to a low enough temperature. If water is put into a freezer it changes to ice.