Torque is the rotational equivalent of linear force. It describes how much a force causes an object to rotate.
Formula
τ = F × d × sin(θ)
Where τ = torque, F = force applied, d = distance from the axis (lever arm), θ = angle between force and lever arm.
Units
- SI: Newton-meters (N·m)
- Imperial: Foot-pounds (ft·lbs)
Real-World Applications
Torque is used when tightening bolts (torque wrenches), measuring engine performance, and designing mechanical systems. Engine torque determines acceleration capability.
Torque vs. Horsepower in Vehicles
Torque determines how quickly a vehicle accelerates from a stop (pulling power); horsepower (which factors in torque × engine speed) determines top-end performance and towing capability at higher RPM. This is why diesel trucks — built for high torque at low RPM — excel at towing, while high-revving sports car engines prioritize horsepower for top speed.
Torque Wrench Settings
Manufacturers specify exact torque values (in ft-lbs or N·m) for critical fasteners like lug nuts and head bolts. Under-tightening risks parts loosening under vibration; over-tightening can strip threads or warp components — which is why torque wrenches, not just "hand-tight plus a bit," are standard in automotive and mechanical assembly.