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!

Homework Help: Angular momentum equation

  1. Aug 26, 2011 #1
    1. The problem statement, all variables and given/known data

    I found this in Goldstein, Poole, and Safko and have seen it in other books. What I don't understand is how the equation gets from the second expression to the third; specifically, why is the m divided by two in the last expression? I am at a loss on this but I know it is not a typo.

    2. Relevant equations
    [tex]\int \mathbf{F} \cdot d\mathbf{s} = m \int \frac{d\mathbf{v}}{dt} \cdot \mathbf{v} dt = \frac{m}{2} \int \frac{d}{dt}(v^2)dt [/tex]
  2. jcsd
  3. Aug 26, 2011 #2


    User Avatar

    Staff: Mentor

    [tex]\frac{d \; v^2}{dt} = 2 v \frac{d v}{dt} [/tex]
    so to make this simply [itex]\frac{dv}{dt} v[/itex] it needs to be divided by two.
  4. Aug 26, 2011 #3
    Thanks, I knew it was something simple that I just could not see.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook