Wind is the movement of air caused by differences in air pressure within the earth's atmosphere. It is largely due to the differences in the barometric pressures in a general area from place to place. The greater the difference, or gradient, the greater the wind speed. Conversely, the wider the spread of pressure readings, the less the wind velocity. Wind, the primary transporter of air masses and precipitation, is an important control in the climates of the earth and in determining local weather conditions from day to day.
Wind speeds and directions have always played significant roles in determining various aspects of history and human geography. They have been prime factors in the sea-age era of exploration and discovery of new lands. They have contributed to the outcomes of military battles. Strong wind conditions have caused deaths and injuries on land, sea, and in the air. High wind velocities have delayed landings of spacecraft. Wind is a key consideration in making navigational plans: Pilots know that it takes less fuel and time to fly from west to east with a tailwind than from east to west against a headwind. These tend to be the prevailing wind directions in the middle latitudes.
Winds have been welcomed when they serve to drive away smog and atmospheric pollutants or bring gentle seabreezes on shore, but unwelcomed when they impact upon the quality of play at a sporting event, or when they dismantle buildings or spread fires. For many centuries, prior to the advent of rural electrification, wind has been used to power windmills, enabling the grinding of grain or the pumping of water. They were first used in Persia in A.D. 644.
Winds have always been a driving force for sailing vessels. Experienced sailors know how to catch a favorable wind so as to maneuver