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Dot Product of Derivatives

  1. Oct 9, 2009 #1
    Hi,
    Im having trouble understanding something in one of my Dynamics lectures.
    The lecturer said that:

    dr/dt dotted with d2r/dt2 (where r is a vector)

    equals: (1/2)(d/dt(dr/dt dotted with dr/dt))...

    I just cant get this result. I know it has something to do with the product rule.

    Thanks for your help, and sorry for the crudity of my notation :-p

    teeeeee
     
  2. jcsd
  3. Oct 9, 2009 #2

    cristo

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    It does. Have you tried evaluating [tex]\frac{dr}{dt}\cdot\frac{dr}{dt}[/tex] using the product rule? What do you get?
     
  4. Oct 9, 2009 #3

    HallsofIvy

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    I believe Cristo meant evaluating
    [tex]\frac{d}{dt}\left(\frac{dr}{dt}\cdot\frac{dr}{dt}\right)[/tex]
     
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