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Dtheta / dt?

  1. Oct 11, 2009 #1
    1. The problem statement, all variables and given/known data


    just a conceptual thing I don't quite understand..
    how come dtheta/dt = v/r? I thought it was basically the same thing as v = r/t, but with radians..
    thanks

    2. Relevant equations



    3. The attempt at a solution
     
    Last edited: Oct 11, 2009
  2. jcsd
  3. Oct 11, 2009 #2

    rock.freak667

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    Re: dtheta/dt?

    ω=dθ/dt

    now θ is the angle of an arc of a circle of radius r and arc length l.

    so θ=l/r

    So ω=d/dt(l/r)

    r doesn't change so
    rω=dl/dt

    and dl/dt=v

    so rω=v
     
  4. Oct 11, 2009 #3
    Re: dtheta/dt?

    Hi, thanks a lot for the reply. Do we say θ=l/r because the arc length might not be in radians?

    thanks
     
  5. Oct 11, 2009 #4

    rock.freak667

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    Re: dtheta/dt?

    Are length is defined as l=rθ when θ is in radians.
     
  6. Oct 11, 2009 #5
    Re: dtheta/dt?

    EDIT: oh never mind, I've got it.. I've somehow forgotten that a radius could be more than 1 unit :P


    thanks!
     
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