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: Equilibrium between 1 stationary mass and 1 orbiting mass

  1. Jun 4, 2010 #1
    I am trying to find the easiest and simplest way of calculating the distance that two celestial bodies would need to be apart, in order for those celestial bodies to never get closer or further away from each other. I have the values of the mass, density, radius, volume and gravity of the two celestial bodies, is it possible to use the values I have to work out how far apart they would need to be to remain in a state of equilibrium? The smaller mass(M1) is orbiting around the larger mass(M2).

    I tried to use the following equation, but to no avail because I neither have the gravitational force(F) nor do I have the radial distance (r) between the masses.

    Newton's law of gravity: F = (M1 * M2) / r^12

    I am looking for an equation that will help me to solve this problem for all planetary bodies.
    Thanks for any and all help. Please keep answers as simple as possible :D
  2. jcsd
  3. Jun 4, 2010 #2


    User Avatar
    Homework Helper

    You'd need to find where the centripetal force = Gravitational force.

    But you would need something like the orbital period to get the distance.

    EDIT: Use the original thread where ehild is helping you
    Last edited: Jun 4, 2010
  4. Jun 4, 2010 #3


    User Avatar
    Homework Helper

    Your question has not much sense in the language of Physics. I tried to explain the situation which is real and seemed to relate to your problem.

    The answer to your question is that there is no such universal distance for the case of two bodies but infinity.

  5. Jun 4, 2010 #4
    I sincerely thank you for trying to help ehild. At least you tried :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook