1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

On torque and work having same units

  1. Apr 22, 2008 #1
    In rotational motion ,

    the units for torque, [itex] \tau = r \times F [/itex],

    are N [itex]\cdot[/itex] m

    and for work done by a torque,

    [itex]W = \int_{\theta1}^{\theta2} \tau \cdot d\theta [/itex], 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)

  2. jcsd
  3. Apr 22, 2008 #2

    Shooting Star

    User Avatar
    Homework Helper

    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" [Broken].
    Last edited by a moderator: May 3, 2017
  4. Apr 24, 2008 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    N-m or N*m would be even better.
  5. Apr 25, 2008 #4
    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??
  6. Apr 25, 2008 #5


    User Avatar

    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).
  7. Apr 26, 2008 #6
    Thanks guys, you're help is very appreciated.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook