Wind is created by changes in air pressure from one area to another. Changes in air pressure are determined by a variety of forces, including the density and temperature of air masses. When air moves from between areas of high pressure and low pressure, wind directions and speeds may change.
The driving force behind changes in air pressure and therefore the creation of wind is gravity. Gravity creates air pressure through the compression of the atmosphere. The force that creates these changes in air pressure is known as the Pressure Gradient Force and is driven by changes in the temperature of the earth's surface.
The movement of air from warm to cold areas causes a rotation of air, or wind. Warm air is less dense than cold air and accumulates at lower altitudes while denser, colder air accumulates at the poles. Changes in air pressure also determine the speed of wind. As air moves gradually from one pressure gradient to another, light winds are created.
Air that moves quickly from one pressure gradient to another creates fast, or strong, winds. The speed of wind is also determined by a deflection of wind's straight pattern along the earth's surface, known as the Coriolis effect, as well as friction that causes it to slow down.