Why does the bottom of a swimming pool always appear shallower than it actually is

The refraction of light at the surface of water makes ponds and swimming pools appear shallower than they really are.

Explanation:

so its just the refraction of light at the surface

The refraction of light at the surface of water makes ponds and swimming pools appear shallower than they really are. If you look at a stick that is poking into some water at an angle the stick looks bent because of refraction. The bottom of the stick seems to be nearer the surface of the water than it really is.

Explanation:

pe = weightxheight = 2000x1000=2,000,000joules

double the distance = divide strength by 4