What is evaporation?
Evaporation is the process by which a liquid turns into a gas at its surface. It happens when some molecules gain enough energy to escape into the air, even below boiling point.
In a liquid, molecules are always moving at different speeds. Those near the surface that move fast enough can break free from their neighbors and escape as vapor. This is why puddles dry up and wet clothes dry on a line, even on cool days. Boiling, by contrast, happens throughout a liquid when it reaches a certain temperature.
Several factors speed up evaporation: higher temperature, a larger surface area, lower humidity and moving air. That is why laundry dries faster on a warm, windy day, and why spreading out a spill helps it dry. Evaporation is a key step in the water cycle, lifting water from oceans into the air.
Evaporation cools
Because the fastest molecules escape, the remaining liquid loses energy and becomes cooler. Sweating cools the body this way. Clay pots and desert coolers use the same principle, and feeling cold after getting out of a swimming pool is caused by water evaporating from your skin.
Did You Know?
Sea salt is often made by letting seawater evaporate in shallow pools under the sun, leaving salt crystals behind.