A nice breeze on a hot summer day is one of life's simple pleasures, but where does that pleasant wind come from? The answer starts at the equator and the poles. When air warms, it expands allowing it to become less dense and rise. The same thing happens to cool air, but opposite the process. So this causes a pressure difference between the poles and the equator causing cool winds to move away from the poles staying close to the ground and the warm air to move away at higher altitudes. This makes a circular motion. Now, because of this circular movement and the way that the Earth spins, the two motions come together to cause a lateral force that results in the wind moving around the Earth instead of just hanging out between the poles and the equator.