There are a couple of demonstrations included on this film which fit snugly into this topic.
Expanding Marshmallows starts about 3½ min into the film and shows how the air trapped inside marshmallows will expand significantly if the air pressure outside is reduced, it’s a great demonstration.
It is also an experiment that can be carried out quickly and easily by students using small marshmallows (the type used on top of hot drinks) and 10 or 20cm3 plastic syringes.
1. After removing the plunger, put the marshmallow into the syringe.
2. Replace the plunger and gently push it up until it is just below the marshmallow.
3. Putting the finger over the open end of the syringe, pull down on the plunger whilst observing the marshmallow expand.
4. The marshmallow shrinks rapidly when the finger is removed.
5. Similarly, using the plunger to compress a syringe full of air will shrink the marshmallow and it will now expand when the finger is removed.
The Cartesian Diver starts about 8½ min into the film and it is excellent for showing the effect of pressure in liquids. It’s good to demonstrate it with a test tube inside a two litre bottle so that students can see the air bubble changing size. Once they've seen this they could carry out the experiment for themselves, perhaps using sauce sachets which are easier to handle than the tubes.