Scuba diver in a bottle

Rang a Trí conducted an experiment to investigate how a scuba diver sinks! Pupils learned that the compression of gases causes the scuba diver to sink!

When the bottle is squeezed, the water pressure increases and the water is forced up into the straw which compresses the air bubble formed in the straw.
As the air bubble gets smaller, the density of the diver increases and the diver sinks!
When you release the bottle, the pressure lessens and the water moves back out of the straw. The air bubble in the straw returns to its original size causing the diver to become less dense and float back to the top of the bottle!