Why does legs appear shorter under the swimming pool?

When light passes from one medium to another, it bends or refracts. This is because the speed of light is different in different media. In air, light travels at about 300,000 kilometers per second. In water, light travels at about 225,000 kilometers per second.

When light strikes the surface of the water at an angle, it refracts and bends towards the normal. The normal is an imaginary line that is perpendicular to the surface of the water. The amount of refraction depends on the angle at which the light strikes the surface of the water. The greater the angle of incidence, the greater the amount of refraction.

When you look at your legs in the swimming pool, you are seeing them through a layer of water. The light from your legs refracts as it passes from the water to the air. This refraction causes your legs to appear shorter than they actually are.