Torque Main Page

The tendency of a force to cause an object to rotate about some axis is measured by a quantity called torque.

Torque = (Force)(Distance)

The symbol used for torque is the Greek letter tau.

When tightening a bolt or a nut a mechanic will determine the amount of torque on the bolt or nut with a tool called a torque wrench.  In the United States of America the common unit for torque is the foot-pound. The SI unit is the N-m or m-N.

1 foot-pound is the amount of torque caused by applying 1 pound of force at a distance of 1 foot.  The force is perpendicular to the lever arm.

The lever arm is often called the moment arm.

If the torque is in a clockwise direction its direction is negative.
If the torque is in a counterclockwise direction its direction is positive.