Torque is a measure of the forces that cause an object to rotate. This measurement is a combination of two concerns:

1. The amount of force applied to cause an object to turn on an axis.

2. The distance between the object’s axis and the point at which the force is applied.

Torque is the product of these two measurements -- a force and a length -- expressed in pound-feet or foot-pounds.

When torque is very small, it is expressed in ounce-inches or inch-ounces. Consider a bolt that must be tightened: If 20 pounds of force is applied to the end of a two-foot wrench, then a torque of 40 foot-pounds has been applied.

Because torque relies on two interrelated measurements -- a force and a length -- a proportional relationship exists when one measurement increases or decreases.

For example, if one doubles the distance between the axis of rotation and the point at which an unchanging force is applied, the torque is also doubled. Similarly, if the distance is halved, the torque is also halved.

Torque is sometimes referred to as a moment, and the distance between an object’s axis of rotation and the point at which a perpendicular force is applied to turn the object is referred to as the moment arm. Thus, an application that requires a torque of 100 foot-pounds also requires a moment of 100 foot-pounds.

There are two types of torque:

1. Reaction torque

2. Rotary torque

See also: What is reaction torque? and What is rotary torque?