Diving and resurfacing jellyfish

A water investigation:

Can we get a jellyfish to sink, and then resurface?

Teacher has a jellyfish.

When we put it in a bottle of water it floats.

We think that this is because the head of the jellyfish is full of air.

Teacher wanted us to get the jellyfish to sink to the bottom and to resurface again.

What could we do?

We could shake the bottle, push the jellyfish with our fingers, roll the bottle, tilt the bottle OR  ???

We figured that if we squeeze the bottle the air in the head of the jellyfish would become a little squashed (or compressed).

This would allow some water to get into the head and be heavy enough to sink the jellyfish.

Now to make him resurface again........

Stop squeezing the bottle and the air will have space to expand again, push the water out of the head of the jellyfish.

Now the jellyfish can swim to the top again.

If you have no jellyfish, teacher showed us a way to make a diver of our own from a lid of a pen, a paper clip and an elastic band.  This works just as well as the jellyfish!