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: Central field - equation

  1. Nov 24, 2007 #1
    1. The problem statement, all variables and given/known data

    Show that in a central force field [tex]\vec{F}(\vec{r})=f(r)\frac{\vec{r}}{r}[/tex] the equation for a body's trajectory in terms of [tex]u=\frac{1}{r}[/tex] is given by:

    where m is the body's mass and L is the angular momentum

    2. Relevant equations

    3. The attempt at a solution

    Transforming Newton's equations for [tex]\ddot{r}[/tex] leads to ab equation for [tex]\ddot{u}[/tex] and [tex]u[/tex] where unfortunately [tex]\dot{u}[/tex] also appears and I don't know how to eliminate it from the equation.
  2. jcsd
  3. Nov 25, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper

    can you show us how you did it?
  4. Nov 25, 2007 #3
    [tex]\ddot u=\frac{d^2u}{d\theta^2}[/tex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook