Difference Between Power and Torque

Power vs Torque

Torque and power are two terms commonly misunderstood even by engineers, leave alone common people. Both terms describe the ability of a device to do work, but whereas torque is the twisting force applied to an object, power is the application of work within a finite time. Power of an engine is always dependent upon torque which is clear from the following equation.

HP= Torque*RPM/5252

An engine produces power by providing a rotating shaft that can exert a given amount of torque on a load at a given RPM. The amount of torque an engine can exert varies at different RPM. The term torque is meaningless for an engine at rest. Torque is the twisting force an engine can generate, and it can generate such a force only when the engine is moving at a good speed which is measured in terms of revolutions per minute. When we are riding a motorcycle or driving a car, every time we change up a gear, we are trading torque for RPM. The twisting force goes down for a while when we increase the gear. This is where power comes in. Power is a combination of torque and RPM. An engine can produce little torque at the crankshaft but can still produce a lot of power if it has high revs. Also, an engine may not have high revs but can produce high torque if it has enough power.

Torque is rotational power of an engine and is measured in Newton meters. Also known as moment or couple, torque originated with the work of Archimedes work on levers.

Talking of differences, torque is rotational version of force, while power is force multiplied by speed.

Torque increases as revs increase from idle to a certain figure after which it falls even if revs increase. Maximum acceleration is reached when maximum torque is attained. On the other hand, power increases with revs up to and past the point of maximum torque. But at still higher revs, torques decreases decreasing power also.