Newton metre

Newton metre is a unit of torque (also called "moment") in the SI system.^[1] The symbolic form is N m or N·m,^[2] and sometimes hyphenated newton-metre. One newton metre is equal to the torque resulting from a force of one newton applied perpendicularly to a moment arm which is one metre long.

A newton metre is dimensionally equal to a joule, the SI unit of energy and work. However, it is not appropriate to express a torque in joules — the units are necessary to distinguish a torque quantity from an energy quantity.^[3] The two quantities, torque and energy, are physically different despite being dimensionally equivalent. For example, energy is a scalar while torque is a vector (in fact, a pseudovector). Also, a given force applied to an object can contribute torque but not work, or work but not torque, or both, or neither.

On the other hand, there are relations between torque and energy that sheds light on their dimensional relationship. In particular, a torque can contribute to rotational energy; the work done in this process (measured in J) is equal to the torque (measured in N m) times the angle through which the body rotates in the direction of the torque.^[4] This accounts for the use of an alternative unit for torque, Joule per radian (J/rad)

Conversion factors

• 1 joule = 1 N·m
• 1 newton metre = 0.7375621 foot-pound force (often "foot-pound")
• 1 metre kilogram-force = 9.80665 N·m
• 1 centimetre kilogram-force = 98.0665 mN·m
• 1 foot-pound force (often "foot-pounds") = 1 pound-force foot (often "pound-feet") ≈ 1.3558 N·m
• 1 inch ounce-force = 7.0615518 mN·m
• 1 dyne centimetre = 10⁻⁷ N·m

See also

• Foot-pound force
• Spring scale
• Torque
• Torque tester

References