Torque is the twisting or turning effort. The torque is equal to the product of the force and its perpendicular 1/2 m distance to the point of rotation. It may or may not result in motion. Power is something else again. It is the rate at which work is being done, and this means something must be moving.
You apply torque to the nut while tightening it on the bolt. You apply torque to the steering wheel while turning the car. Torque is required while turning the car wheels on the road. More torque is required when the car is going up a slope.
Torque can be defined mathematically as “the rate of change of the angular momentum of an object”. The definition of torque states “one or both of the moment of inertia angular or the velocity of an object is changing”. The moment is the general term used for “tendency of one or more applied forces to rotate an object about an axis, but not necessarily to change the angular momentum of the object”.
Torque is measured in N-m.
For example, a rotational force applied to the shaft causing acceleration, such as a drill bit accelerating from the rest position, results in a moment called a torque. By contrast, a lateral force on a beam produces a moment (Also called a bending moment), but since the angular momentum of the beam is not changing, this bending moment is not called a torque. Similarly, with any force couple on an object that has no change to its angular momentum, such a moment is also not called a torque.
If a 20 N force is applied on the shaft through a crank radius of 1/2 m to rotate a wheel, you would be applying 20 x = lO N-m of torque to the crank. You would Dappiying this torque regardless of whether or not the crank was turning and so long as you continue to apply the 20 N force to the crank handle.