# 21.2: Introduction

- Page ID
- 29235

Torque is force acting at a distance, tending to cause rotation around a point. The point about which the object rotates, the pivot point, is called the fulcrum. When force is applied perpendicular to a lever arm, the amount of torque depends on the perpendicular force (F) applied and the length of the lever arm (d) through which the force acts.

**Torque:**

\[\tau = Fd \nonumber \]

**Weight Force:**

\[W = mg \nonumber \]

The amount of torque on one side of a fulcrum is equal and opposite to the amount of torque on the other side of the fulcrum. This can allow a see-saw to be balanced if the two people sit at the correct distances from the pivot point.

\[\tau_1 = -\tau_2 \nonumber \]

Although the torque on each side of the pivot point is equal, the amount of force on each side of the pivot can be very different.