Torque
Definition
The turning effect of a force — what makes wrenches, doorknobs, and seesaws work. Push farther from the pivot and the same force turns harder.
Symbol: · Unit: newton-meter (N·m)
Technical definition
The rotational analogue of force, τ = rF sin θ, where r is the lever arm from the pivot and θ is the angle between the position vector and the force. Torque equals the rate of change of angular momentum.
Example
Pushing a door 0.8 m from its hinges with 25 N of force produces 20 N·m of torque. Push only 0.2 m from the hinges and you need four times the force for the same swing — which is why doorknobs sit at the far edge.
Torque is not force. A huge force applied right at the pivot (r = 0) produces zero torque and zero rotation — that is why a door will not budge if you push on its hinge side. Torque also has a direction (clockwise vs counterclockwise), while work — which shares the N·m unit — is a scalar. Same units, different quantities.