Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Hi, I am a new member (gravity as a function of density)

  1. Jan 14, 2017 #1
    Hi All:
    I am a new member and was recently reviewing a discussion concerning gravity as a function of density. One person had proposed that the force of gravity could also be measured even if the distance from the center was less than the object's radius (inside the sphere). Another proposed that regardless as to your distance, once inside the sphere ONLY the mass between you and its center can effect you; that somehow the mass outside of this 'imaginary' sphere cancelled out...
    This got me thinking about a Black Hole. What if the latter were true and that once you've crossed the Event Horizon, the amount of gravity that 'effects' you becomes less and less as you approach the center...
  2. jcsd
  3. Jan 14, 2017 #2


    User Avatar
    Science Advisor
    Gold Member

    Hi ST_Pete, welcome to PF

    This subforum's function is solely to allow introductions. Any substantive question should be posted in the appropriate forum (in this case, general or classical physics).

    But so as to help you on you way, I'd suggest reading about Newton's shell theorem first (wikipedia has a good article, and there's probably a number of videos on youtube too). You'll see that both the persons you mentioned were right, and perhaps you'll manage to apply it to the case of a BH yourself (keep in mind where all the mass is concentrated in a BH).

    If you'll have any more questions regarding the above, do post them in a separate thread.
  4. Jan 14, 2017 #3
    Thanks man... I appreciate it... Sorry... Didn't know the protocol... The thread said that I had insufficient privileges to reply there so I figured I'd 'wing it' here... My Bad...
  5. Jan 14, 2017 #4


    User Avatar

    Staff: Mentor

    Welcome to the PF. :smile:
    The thread may have been closed because it was old, or perhaps there was some rules violation that got it closed. If you look above the first post in the thread, there is probably a note that says the thread is "Not open for new replies". And if you look at the last post in the thread, there will either be a Mentor note about why the thread was closed, or if there is no such post, the thread is probably old.
  6. Jan 14, 2017 #5
    Thanks man... Yep... Didn't think to look for that... You are probably correct...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted