Final answer:
Objects appear closer when observed underwater due to the refraction of light, which causes light to bend toward the normal when transitioning from water to air.
Step-by-step explanation:
When you look into water in a swimming pool, objects on the bottom often appear to be closer to you than they really are due to the refraction of light. This optical phenomenon occurs when light waves travel from one medium to another with a different density, in this case from water to air. The light bends toward the normal as it passes from the more dense water to the less dense air, causing the object to appear at a location that is higher, or closer, than it actually is. This behavior of light can also explain why a person's legs appear shortened when they are partially submerged in water. Refraction makes the underwater segments of the legs appear to bend towards the observer, giving the illusion of shorter limbs.