1. Not finding help here? Sign up for a free 30min 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!

Why does (dr/dt)*θ = 0 when deriving Velocity?

  1. Feb 9, 2012 #1
    The problem statement, all variables and given/known data


    A derivation of Instantaneous Velocity

    Arc length = s = θ * r

    ds/dt = d(θr)/dt = Instantaneous V

    Product rule:

    V[itex]_{t}[/itex] = (dθ/dt)*r + (dr/dt)*θ

    V[itex]_{t}[/itex] = (dθ/dt)*r + 0

    V[itex]_{t}[/itex] = ωr




    Question:

    Why does dr/dt*θ = 0 ?
     
  2. jcsd
  3. Feb 9, 2012 #2
    Since r is constant, the rate of change of the radius with respect to time (or anything for that matter) is going to be 0.
     
  4. Feb 9, 2012 #3
    ah makes perfect sense, thanks.
     
  5. Feb 9, 2012 #4
    No problem, sir. Good luck.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook