A torque is a vector product of force and radial distance that measures the tendency of a force to rotate an object about an axis or centre. A dynamometer is a device for measuring mechanical force, or power, transmitted by a rotating shaft. Since power is the product of torque and angular speed, all power-measuring dynamometers are essentially torque-measuring devices; the shaft speed is measured separately.
Power-measuring dynamometers may be transmission dynamometers or absorption dynamometers. The former utilize devices that measure torque, in terms of the elastic twist of the shaft or of a special torque-meter inserted between sections of the shaft. The torque is produced by the useful load that the prime mover, motor, or machine is carrying. Absorption dynamometers, on the other hand, produce the torque that they measure by creating a constant restraint to the turning of a shaft by either mechanical friction, fluid friction, or electromagnetic induction.
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