i. Torque: A torque is a force that rotates an axle or wheel around its center.Tthe object must be able to rotate about some center point. By applying a force on the edge of a wheel, you create a torque that rotates the wheel. Likewise, by applying a force on a wrench, you can rotate a bolt within its hole.


The relationship between torque and force is:

T = FR
or
F = T/R


where
  • T is the torque in foot-pounds or newton-meters
  • F is the force in pounds or newtons
  • R is the radius or distance from the center to the edge in feet or meters
  • FR is F times R
  • T/R is T divided by R
R is also sometimes called the moment arm. The force, F, is applied perpendicular to the radius, lever or moment arm.
If the force on a wrench is 10 pounds and the length of the wrench is 6 inches, the torque created is 10 pounds times 0.5 foot = 5 foot-pounds.
If the force on the wrench is 0.5 newtons and the length of the wrench is 20 centimeters, the torque created is 0.5 newtons times 0.2 meters = 0.1 newton-meters.
A torque on the axle of a wheel can be transferred into a force on the circumference of the wheel.
You can demonstrate this force by placing a bicycle up-side-down and spinning one of its wheels. Touching the outer surface of the wheel, you can feel the force pushing your hand in the direction of rotation.