What is torque

The net force acting on a body accelerates it and takes something to give the body an angular acceleration. It needs a force, but it needs to be applied in a way that creates a twisting or turning action. Torque, τ is the rotational version of force and results from the application of one or more forces and is specified relative to a chosen rotation axis or pivot.

Torque is a measure of how much force an object act causes the object to rotate.

Torque is dependent upon :
  • The distance from the rotation axis to the force application point (Refer to the first figure).
  • The magnitude of the force, F.
  • The orientation of the force relative to the displacement from the axis to force application point (Refer to the second figure).

The torque that a force produces is defined by 
τ = R x F 

τ = R x F sinθ

In other words, torque is the cross product between the vector of distance (the distance from the pivot to the point where force is applied) and the vector of force, 'θ' being the angle between r and F.

Example :
Let’s say we’re using a 0.5m long wrench to tighten a wheel nut, and we need to lean on the far end of the wrench with a force of 50 Newtons to do it up tightly. Simply multiplying the two numbers give us the required torque figure in Newton meters.

Torque τ = 50 (N) x 0.5 (m) x = 25 Nm
The SI units of torque are Newton-meter (N.m).
Rotational Equilibrium is analogous to transnational equilibrium, where the sum of the forces is equal to zero. 

There may be more than one force that acts on an object, and each of these forces may act on an object at a different point. Then every force is going to cause torque. The net torque is the sum of the torques in each case.

The sum of the torques is equal to zero in rotational equilibrium. In other words, the object does not have a net torque.

∑τ = 0