Displacement of water.

When you dive into a swimming pool some of the water splashes out over the side.

Your body – no this is not a comment upon your shape or size – needs the space, so the water has to move out of the way.

That’s why concrete is not a good substitute for water in a pool….aaagh!

And, that is also why we need superheroes like NanoParticleMan who can dive right through solid objects.

Especially true if we want to sell solid swimming pools successfully….