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# 21.2: Introduction


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.