The unit for the moment (torque) is derived from the base units "force" and "path".

If the force acts on a rigid body with a fixed axis of rotation, then this body is not displaced, but set in a rotational movement.

In this case it is not only the amount of force, but also the distance of the force application point to the rotation axis of importance: The greater the distance, the greater the effect of rotation (rotational acceleration).

The moment is defined by force times lever arm.

The influence of the rotational movement also occurs when a pair of forces effects a rigid body instead of a single force.

The pure rotational motion without displacement occurs when the both forces are opposit and equal in size.

This force pair is always available at one moment (torque): for a rotating body to which a force acts, the bearing reaction force forms the opposing force, which is exactly the same size, but acts at a certain lever distance.

Therefore one could say: a moment is a force couple.

In the technics it is distinguished between:

- drive torque (in a machine that gives off power),
- output torque (in a machine which receives power).

If the force couple (moment) does not trigger rotational movement, then it is not torque but moment. Depending on the type of mechanical load it is technically distinguished between:

- bending moment,
- torsional moment.

The unit newton meter for the moment (torque) is derived from the Si units for force (Newton) and length (meters).

Metric units |
UK and US units |
---|---|

1 Newtonmeter (Nm) |
0,7375621 pound force feet (lbf ft) |

1 Newtonmeter (Nm) |
8,8507458 pound force inch (lbf in) |

1 Newtonmeter (Nm) |
11,800994 ounce force feet (ozf ft) |

1 Newtonmeter (Nm) |
141,61193 ounce force inch (ozf in) |

1 Newtonmeter (Nm) |
0,04214011 poundal feet (pdl ft) |

UK and US units |
Metric units |
---|---|

1 pound force feet (lbf ft) |
1,355818 Newtonmeter (Nm) |

1 pound force inch (lbf in) |
0,11298483 Newtonmeter (Nm) |

1 ounce force feet (ozf ft) |
0,0847386 Newtonmeter (Nm) |

1 ounce force inch (ozf in) |
0,007061552 Newtonmeter (Nm) |

1 poundal feet (pdl ft) |
23,73036 Newtonmeter (Nm) |