counterweight

Simple Crane

A counterweight is an equivalent counterbalancing weight that balances a load.^[1]

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.^[2]

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.^[3][4]

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.^[5]

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 power 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.^[6]

Space elevator: A space elevator is a proposed structure designed to transport material from a celestial body's surface into space. Many variants have been proposed, but the concept most often refers to an elevator that reaches from the surface of the Earth to geostationary outer space, with a counterweight attached at its outer end.

By attaching a counterweight at the end, inertia ensures that the cable remains stretched taut, countering the gravitational pull on the lower sections and thereby allowing the elevator to remain in geostationary orbit.

The counterweight itself could assume one of several forms:

1. a heavy, captured asteroid (as shown in the diagram);
2. a space dock, space station or spaceport positioned past geostationary orbit; or
3. an extension of the cable itself far beyond geostationary orbit.

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.^[7]

Concrete counterweights on a tower crane

Crane (machine): 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.^[8] The short arm is called the machinery arm; this holds the motors and electronics to operate the crane, as well as the concrete counterweights.^[9]

• Vertical lift bridge
• Drawbridge
• Bascule bridge

References

External links

• Media related to Counterweights at Wikimedia Commons