Definitions

Counterweight

Counterweight

[koun-ter-weyt]

A counterweight is an equivalent counterbalancing weight that balances a load.

Uses

A counterweight is 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.

Counterweights in action

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 car, so the motor only has to lift the difference between the car load and the counterweight load. The counterweight also increases the ascending acceleration force and decreases the descending acceleration force to reduce the amount of horsepower needed by the motor. The elevator car and the counterweights both have rollers attached to them to prevent irregular movement and provide a smoother ride for the passengers.

Metronome

A wind-up mechanical metronome has an adjustable weight and spring mechanism that allows the speed to be adjusted by placement of the weight on the spindle. The tempo speed is decreased by moving the weight to a higher spindle marking or increased by moving it to a lower marking.

Tower Cranes

The tower crane (see picture) is a modern form of balance crane that is fixed to the ground. A horizontal boom is balanced asymmetrically across the top of the tower. The long arm carries the lifting gear. The short arm is called the machinery arm; this holds the motors and electronics to operate the crane, as well as the concrete counterweights.

Vertical lift bridge

Drawbridge

Bascule bridge

References

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