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!

Angular acceleration of a planet

  1. Nov 19, 2013 #1
    So my teacher said that an object farther from the center experiences greater centripetal acceleration. How is that possible? lets say we have a sun + planet system. F = GmM/r^2 so when the planet's r is greater, wouldn't the force become lower compared to the planet being closer to the sun?
  2. jcsd
  3. Nov 19, 2013 #2
    When the planet's r is greater... the fource would become lower compared to the planet being FARTHER from the sun.

    Also, call it star, not Sun. The Sun is our star
  4. Nov 19, 2013 #3
    What if it was a ball attached to a string? How would that be different from a binary planet-star system?
  5. Nov 19, 2013 #4
    The planet would have smaller centripetal acceleration because it would be moving slower than if it was closer to the Sun. It needs less speed to stay in orbit
  6. Nov 20, 2013 #5


    User Avatar
    Gold Member

    Speed isn't a proper term in physics. In the case of circular motion, it's velocity that represents both (1) the rate of motion and (2) the direction.

    Acceleration, on the other hand, is the change in velocity over time. Which is constantly changing direction in circular motion, albeit uniformly.

    PF indicates a larger orbit will have a larger centripetal acceleration. See thread link in my next post.
    Last edited: Nov 20, 2013
  7. Nov 20, 2013 #6


    User Avatar
    Gold Member

    Your teacher is correct. Physics Forum indicates so in a planetary example, but I'm wondering if planet's orbits are a proper example.

    I'm having some doubts about the OP question - if planets are the example the textbook had in mind. If the period of the circular motion stays constant, the acceleration is obviously greater the further from the center. But gravitational orbits...

    There's a homework help thread on this exact question here:

    Hope a PF expert will reply and help sort this out.
    Last edited: Nov 20, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook