Counterweight

A counterweight is a weight that, by exerting an opposite force, provides balance and stability of a mechanical system. Its purpose is to make lifting the load more efficient, which saves energy and is less taxing on the lifting machine.

Counterweights are often used in traction lifts (elevators), cranes and funfair rides. In these applications, the expected load multiplied by the distance that load will be spaced from the central support (called the "tipping point") must be equal to the counterweight's mass times its distance from the tipping point in order to prevent over-balancing either side. This distance times mass is called the load moment.

A counterbalance is a weight or force that balances or offsets another as when two objects of equal weight, power, or influence are acting in opposition to each other. The objects are then said to be in counterbalance.

Trebuchet: There are five major components of a trebuchet: beam, counterweight, frame, guide chute, and sling. After the counterweight drops from a platform on the frame, gravity pulls the counterweight and pivots the beam. Without the counterweight, the beam could not complete the arc that allows the sling to accurately release the projectile.

Crankshaft: 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.

Desk lamp: Some balanced arm lamps work with a counterweight to keep the arm and lamp in the desired position.

Elevator: In traction (non-hydraulic) elevators, a heavy counterweight counterbalances the load of the elevator carriage, so the motor lifts much less of the carriage's weight (specifically, the counterweight is the weight of the carriage plus 40-50% of its rated capacity). The counterweight also increases the ascending acceleration force and decreases the descending acceleration force to reduce the amount of power needed by the motor. The elevator carriage and the counterweights both have wheel roller guides attached to them to prevent irregular movement and provide a smoother ride for the passengers.

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Wikipedia