I’m planning to do a science fair project on scuba diving but I need some ideas to help me get more focused on a really good science fair project related to scuba diving.

Sure, make a cartesian scuba diver!

You’ll need;
one large plastic coke bottle
one large pen top
one paper clip
one fishing weight

o Fill the bottle with water
o Place the paperclip on the pen top, so that the air inside the pentop
makes it float.
o Put the weight on the paperclip, to keep the pentop right-side up
o Float the pentop assembly in the bottle of water
o Put the bottle top back on the bottle

Now, when you squeeze the bottle, you are increasing pressure inside.
The air in the pentop (try to find a clear one) will be compressed.
When the air is compressed, the pentop assy (your diver) will sink!