what is evaporation

Evaporation is the process by which a liquid turns into a gas. It occurs on the surface of a liquid as it changes into the gas phase. When a liquid is heated, its molecules move and vibrate so quickly that they escape into the air as a gas. The sun (solar energy) drives evaporation of water from oceans, lakes, moisture in the soil, and other sources of water. Evaporation is an essential part of the water cycle. In hydrology, evaporation and transpiration (which involves evaporation within plant stomata) are collectively termed evapotranspiration. The escaping molecules accumulate as a vapor above the liquid if evaporation takes place in an enclosed area. Many of the molecules return to the liquid, with returning molecules becoming more frequent as the density and pressure of the vapor increases. When the process of escape and return reaches an equilibrium, the vapor is said to be saturated. The main factors affecting evaporation are temperature (specifically, the temperature difference between the evaporating surface and the air), relative humidity, wind speed, and solar radiation.