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Torque = dL / dt ?

  1. Oct 13, 2015 #1
    I read this article:
    at the bottom of page 2, it bolded text it is said "Torque = rate of change of angular momentum"

    Is that right? It seems to suggest that Torque = (δ Angular momentum) / (δ time)
    but the units do not appear to work out. Torque is in N*m, the right hand side's unit is kg*m^2*s^-2. I don't know anyway this can equate.

    I might have missed something painfully obvious, but I can't see it right now, my head is fried from lack of sleep.
  2. jcsd
  3. Oct 13, 2015 #2
    A Newton is not a base SI unit. You can use Newton's seconds law (##\vec{F} = m\vec{a}##) to find out for yourself.
    You'll see they do match.
  4. Oct 14, 2015 #3


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    Note that since F = dp/dt, the time rate of change of linear momentum, you should notice the angular equivalent of the expression for torque, i.e. T = dL/dt, the time rate of change of angular momentum. Torque is the "force equivalent" in rotational motion.

    There is a completely analogous set of equations between linear motion and angular motion. If you can find the angular equivalent of a linear expression, then the angular kinematics is almost identical.

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