What phenomenon explains why jumping into a pool feels cooler on a hot day?

Jumping into a pool on a hot day feels cooler primarily due to evaporation cooling. When you enter the water, some water molecules on the surface absorb heat from your body and gain enough energy to transition from the liquid phase to the gaseous phase. This process requires energy, which is taken from the surrounding environment—in this case, your body.

As these water molecules evaporate, they carry heat away from your skin, resulting in a cooling effect. This phenomenon is particularly noticeable on a hot day, where the contrast between your body temperature and the cooler water enhances the sensation of coolness. Evaporation is a highly effective cooling mechanism, which is why sweat on our skin also helps to regulate body temperature in warm conditions.

Other options like specific heat capacity relate to the amount of heat energy needed to change the temperature of a substance but do not specifically explain the cool sensation experienced in this scenario. Thermal conductivity pertains to how heat transfers through materials, and while convection currents deal with heat transfer in fluids, they do not account for the immediate cooling effect felt when entering water.