English units of torque are pound-inches or pound-feet; the SI unit is the Newton-meter. Notice that the torque units contain a distance and a force. To calculate the torque, you just multiply the force by the distance from the center. In the case of the lug nuts, if the wrench is a foot long, and you put 200 pounds of force on it, you are generating 200 pound-feet of torque. If you use a 2-foot wrench, you only need to put 100 pounds of force on it to generate the same torque.

The force applied to a lever, multiplied by its distance from the lever's fulcrum, is the torque. As a formula, you can define Torque as :

where,

r is the vector from the axis of rotation to the point on which the force is acting.

F is the vector of force.

Torque is important in the design of machines such as engines. The measurement of torque is also important in automotive engineering, being concerned with the transmission of power from the engine through the drive train to the wheels of a vehicle. Torque (and power output) can be measured with a dynamometer.

A torque wrench is used where the tightness of screws and bolts is crucial. Torque is also the easiest way to explain mechanical advantage in just about every simple machine except the pulley.

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