Counterweight: Encyclopedia - Counterweight

Counterweight

A counterweight is a weight that balances a load. They are often used in traction lifts (elevators), cranes, and funfair rides.

If the counterweight were not there, the load would tend to tip the crane forwards [clockwise]. The counterweight, which is usually made of a dense material such as concrete or lead, provides an anticlockwise moment that balances the load on the crane.

What's more: When the load is lifted, the counterweight is lowered. This reduces the amount of work done.

A counterweight is also used in many rotating systems to reduce vibrations due to imbalances in the rotating assembly. A typical example is counterweights on crankshafts in piston engines.

In traction (non-hydraulic) elevators, a heavy counterweight counterbalances the load of the elevator car, so the motor only has to lift the difference between the car load and the counterweight load.

Adapted from the Wikipedia article "Counterweight", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki