Figure 15 - One big sausage.

Blow up that sausage 2 - When gases are heated they expand. On a sunny day we can show this very simply by filling a sausage shaped plastic bag with air, tying the open end and allowing the sun’s rays to heat it up. See here for a source of large plastic bags (£13).

After a short time feel the bag and describe any changes. What has happened to the air inside? The bag becomes firmer as the warmed air inside expands and pushes against the wall of the bag.

If the sun is sufficiently strong the bag may even lift off the ground because the warmed air trapped in the bag is at a much higher temperature than that outside. Thus it is less dense and therefore rises. See a video of “the sausage” in action.

Snap, crackle & pop