Cracking the SAT Physics Subject Test

(or moment arm) of the force F relative to the pivot and is symbolized by l.

The torque of F is defined as the product

τ = lF

This alternative equation

for torque basically takes

the first equation and

converts a force applied at

an angle to its equivalent

force as if it were applied

perpendicularly to

that object.

(Just as the lever arm is sometimes called the moment arm, the torque is also called
the moment of the force.) The fact that these two definitions of torque, τ = rF sin θ
and τ = lF, are equivalent follows from the fact that l = r sin θ.