Basic Definition and Rotating Beams
Whenever a force is applied to a rigid body (a bar, a beam, a pole) it usually results in the rigid body rotating about an axis or pivot  that is, a torque has been applied.
In the following diagrams, we first see a uniform beam balanced on a knifeedge. This is accomplished by placing the knifeedge in the exact center directly under the beam's center of gravity. If the beam is shifted to either the right or left side of the knifeedge, it will no longer remain in equilibrium since the weight of the beam will be producing a torque. The beam will now be tilted. If a mass having the same weight of the beam is placed equidistant from the pivot on the opposite side, the beam will once again be brought back to equilibrium and return to its original level orientation.
To calculate the magnitude of the torque produced by a force we use the formula or where

F represents the magnitude of applied force

r represents its moment arm

represents the angle formed between F and r
If F and r are mutually perpendicular, sin 90º = 1 and . The magnitude of the moment arm, r, is often written as since it, more often than not, represents a length along a beam. The moment arm is defined as the perpendicular distance from the line of action of the force to the pivot point. Since F is measured in newtons and is in meters, torque is measured in m nt. Alert! torque is not measured in joules, even though a joule equals a newtonmeter. 