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Newton-metre

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SI unit of torque
For the instrument that measures forces in newtons, see Spring scale.
Newton-metre
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
Unit oftorque
SymbolN⋅m, N m
Conversions
1 N⋅m in ...... is equal to ...
   FPS system    0.73756215 lbf.ft
   inch⋅pound-force   8.8507 in lbf
   inch⋅ounce-force    141.6 in oz

The newton-metre or newton-meter (also non-hyphenated, newton metre or newton meter; symbol N⋅m[1] or N m[1] )[a] is the unit of torque (also called moment ) in the International System of Units (SI). 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 unit 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 (i.e. the lever arm length) 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] "Even though torque has the same dimension as energy (SI unit joule), the joule is never used for expressing torque".[4]

Newton-metres and joules are dimensionally equivalent in the sense that they have the same expression in SI base units,

1 N m = 1 kg m 2 s 2 , 1 J = 1 k g m 2 s 2 {\displaystyle 1,円{\text{N}}{\cdot }\mathrm {m} =1,円{\frac {{\text{kg}}{\cdot }{\text{m}}^{2}}{{\text{s}}^{2}}}\quad ,\quad 1,円\mathrm {J} =1,円{\frac {\mathrm {kg} {\cdot }\mathrm {m} ^{2}}{\mathrm {s} ^{2}}}} {\displaystyle 1,円{\text{N}}{\cdot }\mathrm {m} =1,円{\frac {{\text{kg}}{\cdot }{\text{m}}^{2}}{{\text{s}}^{2}}}\quad ,\quad 1,円\mathrm {J} =1,円{\frac {\mathrm {kg} {\cdot }\mathrm {m} ^{2}}{\mathrm {s} ^{2}}}}

but are distinguished in terms of applicable kind of quantity, to avoid misunderstandings when a torque is mistaken for an energy or vice versa. Similar examples of dimensionally equivalent units include Pa versus J/m3, Bq versus Hz, and ohm versus ohm per square.

Conversion factors

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See also

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Notes

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  1. ^ The nonstandard notation "Nm" occurs in some fields.

References

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  1. ^ a b "BIPM – unit symbols". Archived from the original on 2017年10月01日. Retrieved 2016年10月18日.
  2. ^ 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".
  3. ^ Fundamentals of Physics, 9th edition by Halliday Resnick Walker, 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
  4. ^ a b "BIPM - special names". Archived from the original on 2019年03月21日. Retrieved 2015年09月27日.
  5. ^ Mechanical Engineering Formulas Pocket Guide, p6
  6. ^ Concise encyclopedia of plastics, by Donald V. Rosato, Marlene G. Rosato, Dominick V. Rosato, p621

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