Newton metre
The newton metre (also newton-metre, symbol N⋅m,[1] N m[1]) is a unit of torque (also called moment) in the SI system. One newton metre is equal to the torque resulting from a force of one newton applied perpendicularly to the end of a moment arm that is one metre long. The nonstandard symbol Nm occurs in some fields.
Newton metre | |
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One newton-metre is the torque resulting from a force of one newton applied perpendicularly to the end of a moment arm that is one metre long. | |
General information | |
Unit system | SI derived unit |
Unit of | torque |
Symbol | N⋅m or N m |
Conversions | |
1 N⋅m in ... | ... is equal to ... |
FPS system | 0.73756215 ft lbf |
inch⋅pound-force | 8.8507 in lbf |
inch⋅ounce-force | 141.6 in oz |
It is also used less commonly as a unit of work, or energy, in which case it is equivalent to the more common and standard SI unit of energy, the joule.[2] In this usage the metre term represents the distance travelled or displacement in the direction of the force, and not the perpendicular distance from a fulcrum as it does when used to express torque. This usage is generally discouraged,[3] since it can lead to confusion as to whether a given quantity expressed in newton metres is a torque or a quantity of energy.[4] However, since torque represents energy transferred or expended per angle of revolution, one newton metre of torque is equivalent to one joule per radian.[4]
Newton metres and joules are dimensionally equivalent in the sense that they have the same expression in SI base units:
Again, N⋅m and J are distinguished in order to avoid misunderstandings where a torque is mistaken for an energy or vice versa. Similar examples of dimensionally equivalent units include Pa versus J/m^{3}, Bq versus Hz, and ohm versus ohm per square.
Conversion factors
- 1 kilogram-force metre = 9.80665 N⋅m[5][6]
- 1 newton metre ≈ 0.73756215 pound-force-feet
- 1 pound-foot ≡ 1 pound-force-foot ≈ 1.35581795 N⋅m
- 1 ounce-inch ≡ 1 ounce-force-inch ≈ 7.06155181 mN⋅m (milliNewton-metres)
- 1 dyne-centimetre = 10^{−7} N⋅m
See also
- Bending moment
- Spring scale
- Torque tester
- Newton second, the derived SI unit of impulse
References
- BIPM – unit symbols
- For example: Eshbach's handbook of engineering fundamentals - 10.4 Engineering Thermodynamics and Heat Transfer "In SI units the basic unit of energy is newton-metre".
- Fundamentals of Physics, 9th edition by Halliday Resnick Ralker, p. 309. "The SI unit of torque is the newton-meter. In our discussion of energy we called this combination the joule. But torque is not work and torque should be expressed in newton-meters, not joules. google books link
- BIPM - special names
- Mechanical Engineering Formulas Pocket Guide, p6
- Concise encyclopedia of plastics, by Donald V. Rosato, Marlene G. Rosato, Dominick V. Rosato, p621