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In practice, the relationship between power and torque can be observed in bicycles: Bicycles are typically composed of two road wheels, front and rear gears (referred to as sprockets) meshing with a chain, and a derailleur mechanism if the bicycle's transmission system allows multiple gear ratios to be used (i.e. multi-speed bicycle), all of ...
Power in mechanical systems is the combination of forces and movement. In particular, power is the product of a force on an object and the object's velocity, or the product of a torque on a shaft and the shaft's angular velocity. Mechanical power is also described as the time derivative of work.
Engine power is the power that an engine can put out. It can be expressed in power units, most commonly kilowatt, pferdestärke (metric horsepower), or horsepower.In terms of internal combustion engines, the engine power usually describes the rated power, which is a power output that the engine can maintain over a long period of time according to a certain testing method, for example ISO 1585.
The relationship between and is not intuitive, to the point that many people simply assert that torque and are not related at all. An analogy with a hypothetical linear motor can help to convince that it is true.
The forces have a turning effect or moment called a torque about an axis which is normal (perpendicular) to the plane of the forces. The SI unit for the torque of the couple is newton metre. If the two forces are F and −F, then the magnitude of the torque is given by the following formula: = where
The torque is then related to the lever length, shaft diameter and measured force. The device is generally used over a range of engine speeds to obtain power and torque curves for the engine, since there is a non-linear relationship between torque and engine speed for most engine types. Power output in SI units may be calculated as follows:
The moment of force, or torque, is a first moment: =, or, more generally, .; Similarly, angular momentum is the 1st moment of momentum: =.Momentum itself is not a moment.; The electric dipole moment is also a 1st moment: = for two opposite point charges or () for a distributed charge with charge density ().
Speed has dropped out of the equation, and the only variables are the torque and displacement volume. Since the range of maximum brake mean effective pressures for good engine designs is well established, we now have a displacement-independent measure of the torque-producing capacity of an engine design – a specific torque of sorts.