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Angular Momentum in a Kepler Orbit

  1. May 6, 2013 #1
    I got myself here a satellite rotating at a large distance around planet X.

    Distance from center of planet X = 100,
    mass of the satellite = 1 gram (really small),
    mass of planet X = 1.0 kg
    velocity of my satellite 10 m/sec
    and in this oddball universe the gravitational constant = 10**4

    So the satellite-planet X system has an angular momentum of 100 * 10 = 1000 m**2/sec

    Now suddenly I place a second planet, planet Y, right next to planet X

    mass of planet Y = 1 kg

    So at this instant, the central gravitational source is now 2.0 kg but distance is still 100 and velocity of satellite is still 10

    My question : has the angular momentum of the system increased?

    I'd like to use angular momentum conservation to figure the characteristics of a
    satellite / planet / planet trajectory. That's where I'm going with this.
  2. jcsd
  3. May 6, 2013 #2


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    Science Advisor
    Homework Helper

    Hi Rapidrain! :smile:
    Angular momentum = radius "cross" momentum.

    Neither the momentum nor the radius has changed, so the angular momentum is also the same.

    The satellite will follow an ellipse instead of its original circle.
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