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Thread: Angular Momentum

  1. #1
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    Angular Momentum

    So to prove angular momentum (L = r x p) is conserved, I have to prove the derivative of L = 0.

    The proof I have is the derivative of L

    = (ṙ p) + (r ṗ)

    = 0 + r F





    = 0

    (Sorry about the formatting, really new here).

    I don't understand

    1) Why (ṙ p) = 0

    2) Why
    r F = 0

    Thank you so much sorry the formatting is terrible.
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  2. #2
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    Re: Angular Momentum

    Quote Originally Posted by princessp View Post
    So to prove angular momentum (L = r x p) is conserved, I have to prove the derivative of L = 0.

    The proof I have is the derivative of L

    = (ṙ p) + (r ṗ)

    = 0 + r F





    = 0

    (Sorry about the formatting, really new here).

    I don't understand

    1) Why (ṙ p) = 0

    2) Why
    r F = 0

    Thank you so much sorry the formatting is terrible.
    Look at the directions of the vectors.

    $\displaystyle \dot{r} \times p = v_{tan} \times mv$ where $\displaystyle v_{tan}$ is the tangential component of the velocity. What is the term v_{tan} x v equal to?

    $\displaystyle r \times F = r \times F_c$. What direction does the centripetal force have?

    -Dan
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