Even on a warm day, stepping out of a swimming pool can make you shiver. A layer of water remains on your skin and begins to evaporate. Evaporation requires energy. Higher-energy water particles escape into the air, carrying energy away from the water and your skin. Wind speeds up evaporation by removing humid air from near your body, so a breezy poolside often feels colder. Drying yourself with a towel reduces the water available to evaporate and therefore reduces this cooling effect.

The effect becomes easier to notice when conditions change. Temperature, pressure and particle motion can alter how quickly processes happen or how matter behaves. Food storage, refrigeration, cooking and weather all give everyday ways to test the same particle ideas without needing specialist equipment.

Temperature is linked to the average kinetic energy of particles, while internal energy includes the energy associated with their motion and interactions. Heating transfers energy into a material, but that energy does not always raise its temperature: during a change of state it can instead alter the arrangement and separation of particles. Conduction, convection and radiation then determine how quickly energy moves to or from the surroundings.