On torque and work having same units

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    Torque Units Work
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Discussion Overview

The discussion revolves around the relationship between torque and work, specifically addressing whether it is appropriate to express torque in Joules, given that both torque and work share the same SI units (N·m and Joules). The scope includes conceptual clarification and technical reasoning regarding the nature of these quantities in rotational motion.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants note that torque is defined as τ = r × F, with units of N·m, while work done by a torque is expressed as W = ∫(θ1 to θ2) τ · dθ, resulting in Joules.
  • Others argue that torque and work are fundamentally different types of quantities, with work being a scalar and torque being a vector (or pseudo-vector).
  • A participant suggests that using N·m or N*m is preferable for torque, rather than mN.
  • One participant raises an analogy, questioning if the same dimensionality of quantities (like frequency and rate constants) justifies expressing them interchangeably.
  • Another participant acknowledges that while using Joules for torque is possible, it may lead to confusion among others, emphasizing that turning a shaft with a specific torque requires a corresponding amount of energy measured in Joules.

Areas of Agreement / Disagreement

Participants express differing views on whether it is appropriate to use Joules to describe torque. There is no consensus on this issue, as some emphasize the distinction between the two quantities while others highlight their dimensional similarity.

Contextual Notes

The discussion includes assumptions about the definitions and properties of torque and work, as well as the implications of using different units. There are unresolved questions regarding the appropriateness of unit interchangeability based on dimensional analysis.

benabean
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In rotational motion ,

the units for torque, \tau = r \times F,

are N \cdot m


and for work done by a torque,

W = \int_{\theta1}^{\theta2} \tau \cdot d\theta, are Joules.

Yet both these quantities are homongenous/ have same SI units.

Is it so wrong to quote torques in Joules? If so, why?
(And vice versa)

b.
 
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Torque and work are two different types of quantities. Work done done is a scalar quantity, whereas torque is a (pseudo)vector.

As a matter of interest, you are not even supposed to say mN for torque, but Nm.

For more, read http://en.wikipedia.org/wiki/Torque" .
 
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N-m or N*m would be even better.
 
they have the same dimensions, but so do the frequency of a sound wave and the rate constant of a first order chemical reaction. Does that mean you can express a rate constant in Hz??
 
you can use the same units if you want, but it might confuse some folks if you used Joules to describe a measure of torque.

turning a shaft against X Nt-m of torque exactly one radian of twist requires X Joules of energy. measuring angles in radians is dimensionless (being the ratio of like-dimensioned quantities: arc length divided by radius).
 
Thanks guys, you're help is very appreciated.
 

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