An anemometer is an instrument that measures wind speed and wind pressure. Anemometers are important tools for meteorologists, who study weather patterns. They are also important to the work of physicists, who study the way air moves.

The most common type of anemometer has three or four cups attached to horizontal arms. The arms are attached to a vertical rod. As the wind blows, the cups rotate, making the rod spin. The stronger the wind blows, the faster the rod spins. The anemometer counts the number of rotations, or turns, which is used to calculate wind speed. Because wind speeds are not consistent—there are gusts and lulls—wind speed is usually averaged over a short period of time.

A similar type of anemometer counts the revolutions made by windmill-style blades. The rod of windmill anemometers rotates horizontally.

Other anemometers calculate wind speed in different ways. A hot-wire anemometer takes advantage of the fact that air cools a heated object when it flows over it. (That is why a breeze feels refreshing on a hot day.) In a hot-wire anemometer, an electrically heated, thin wire is placed in the wind. The amount of power needed to keep the wire hot is used to calculate the wind speed. The higher the wind speed, the more power is required to keep the wire at a constant temperature.

Wind speed can also be determined by measuring air pressure. (Air pressure itself is measured by an instrument called a barometer.) A tube anemometer uses air pressure to determine the wind pressure, or speed. A tube anemometer measures the air pressure inside a glass tube that is closed at one end. By comparing the air pressure inside the tube to the air pressure outside the tube, wind speed can be calculated.

Other anemometers work by measuring the speed of sound waves or by shining laser beams on tiny particles in the wind and measuring their effect.

Uses of Anemometers

Anemometers are used at almost all weather stations, from the frigid Arctic to warm equatorial regions. Wind speed helps indicate a change in weather patterns, such as an approaching storm, which is important for pilots, engineers, and climatologists.

Aerospace engineers and physicists often use laser anemometers. This type of anemometer is used in velocity experiments. Velocity is the measurement of the rate and direction of change in the position of an object. Laser anemometers calculate the wind speed around cars, airplanes, and spacecraft, for instance. Anemometers help engineers make these vehicles more aerodynamic.