# Torque

Written by Jerry Ratzlaff on . Posted in Classical Mechanics

Torque, abbreviated as $$\tau$$ (Greek symbol tau) or T, also called moment of force, is a rotational moment.  It is a measure of how much twisting is applied to a fastener.  The units used to measure torque are in the form of force times length.  Usually measured in newton-metres (Nm) if metric units are used or pounds feet (lb-ft) when imperial units are used.

## Torque formulas

 $$\large{ \tau = r \; F \; sin \; \theta }$$ $$\large{ \tau = l \; F }$$ $$\large{ \tau = d \; F }$$ $$\large{ \tau = I \; \alpha }$$ $$\large{ \tau = \frac{ 5252\; HP }{ s } }$$ (engine horsepower)

### Where:

$$\large{ \tau }$$  (Greek symbol tau) = torque

$$\large{ \theta }$$  (Greek symbol theta) = angle

$$\large{ \alpha }$$  (Greek symbol alpha) = angular acceleration

$$\large{ d }$$ = diplacement

$$\large{ F }$$ = force

$$\large{ HP }$$ = horsepower

$$\large{ l }$$ = length, moment arm

$$\large{ I }$$ = moment of inertia

$$\large{ P }$$ = power

$$\large{ r }$$ = radius

$$\large{ s }$$ = speed (rpm)

## Breakaway Torque

The torque necessary to put into reverse rotation a bolt that has not been tightened.

## Breakloose Torque

The torque required to effect reverse rotation when a pre-stressed threaded assembly is loosened.