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!

Fel and Fg interaction

  1. Feb 25, 2015 #1
    I did the math and figured that Fel between two protons at 1 mm is 2.307E-22 N, and the Fg at the same distance is 1.867E-36 obviously these values change with the number of protons, and distance. this is an issue because I'm trying to imagine a hypothetical object as charged as possible while still held together by gravity. Assuming uniform distribution of protons and electrons, how many electrons are needed to make The repulsive force of Fel less than the attractive force of gravity on an object primarily comprised of protons? What about an object comprised of electrons?
  2. jcsd
  3. Feb 26, 2015 #2
    The biggest problem i see is that in replacing protons with electrons reduces both repulsive Fel and attractive Fg
  4. Feb 27, 2015 #3
    Atoms and molecules aren't held together by gravity. The force exists, of course, but is negligible compared to the other forces present. They are held together by the electromagnetic force at one level, and the nuclear force (extremely important) at another. Gravity is too weak to be considered here, don't you think? Protons are held together in nuclei not because "surrounding electrons reduce the repulsion between them causing gravity to become more prominent", but because of the strong nuclear force which binds the nucleons together. It is much stronger than the repulsive force between protons.
    Last edited: Feb 27, 2015
  5. Feb 27, 2015 #4


    Staff: Mentor

    Let nP be the number of protons and nE be the number of electrons. Write down an expression for the gravitational force from nP+nE, and an expression for the electrostatic force. Set them equal.

    You now have one equation in two unknowns, so you cannot solve. But you can solve for nE/nP
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook