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

Equivalence of mass, energy and gravity

  1. Apr 22, 2010 #1
    Hi guys, I'd like to hear what you think about a little thing I did talking about the equivalence of mass, energy and gravity. I used planet earth as an example.

    Here's the link to the .docx Word file:
    http://www.angelfire.com/bug/chaos1/Gravity_Rotation.docx" [Broken]

    My premise is that the more energy an object has the more mass, and the more mass the more gravity.

    Thanks. P.S. If you have any problems with the file let me know.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 22, 2010 #2
    Re: Energy-->Mass-->Gravity

    I'll try and find a way to paste the document "as is" so you don't have to go through downloading it. If you know a way to convert it, specifically refering to the equation editor objects in Word please let me know. Thanks.
  4. Jun 4, 2010 #3
    Re: Energy-->Mass-->Gravity

    Alright, I put it picture format, so here it is:
    (Please Comment)

    [PLAIN]http://img72.imageshack.us/img72/7392/gravityrotation.gif [Broken]
    Last edited by a moderator: May 4, 2017
  5. Jun 5, 2010 #4
    Re: Energy-->Mass-->Gravity

    Anyone care to comment?(bump)
  6. Jun 5, 2010 #5
    Re: Energy-->Mass-->Gravity

    Why, after discussing the Relativistic concept of mass-energy equivalence, are you then reverting to Newton's explicitly non-Relativistic theory of gravity?

    Unfortunately, General Relativity is more complicated than replacing "m" by "E" in Newton's equations.
  7. Jun 5, 2010 #6
    Re: Energy-->Mass-->Gravity

    Verry good observation, I'll have to revisit the gravity equations....

    But still, on the main premise, does it add to the gravitational force or not?
  8. Jun 5, 2010 #7
    Re: Energy-->Mass-->Gravity

    Taylor/Wheeler: Spacetime Physics:

    Perhaps the expression "mass-energy equivalence" should be numbered among such slurrings.

    The famous equation E = mc2 can be understood in two ways. Einstein's own preference was to treat mass here as the coordinate-independent kind, sometimes called rest mass; in that case, the equation says that the energy of a system is equal to its mass, times c squared, in a reference frame where the system has no 3-momentum, i.e. its rest frame ( http://physics.princeton.edu/~mcdonald/examples/EM/hecht_ajp_77_804_09.pdf [Broken] ); this is the viewpoint recommended by Taylor and Wheeler who say it's best to dispense with the concept of relativistic mass. Others interpret the famous equation as saying the energy of a massive system equals its relativistic mass times c squared.

    A more revealing equation is m2=E/c2-p2, where m is (rest) mass, E total energy, and p the Euclidean norm (magnitude) of 3-momentum. This also applies to systems with no mass, so the energy of a photon is equal to the magnitude of its 3-momentum.
    Last edited by a moderator: May 4, 2017
  9. Jul 7, 2010 #8
    Re: Energy-->Mass-->Gravity

    Thanks for the replies guys.

    Ok, I'll just leave with this simple question: Does the rotational kinetic energy add to a body's gravity?
  10. Jul 7, 2010 #9
    Re: Energy-->Mass-->Gravity

    Yes. Angular momentum would show up along with pressure and shear stresses.
    The sources of gravity are found in the 16 terms of the Stress-Energy tensor.
    There is part of it that has your mc^2 in it. Other parts capture every other
    kind of energy that will create gravity.

    They are all depicted here: http://en.wikipedia.org/wiki/File:StressEnergyTensor.svg
    Get a good book on General Relativity and it should spell it out for you.
  11. Jul 7, 2010 #10
    Re: Energy-->Mass-->Gravity

    But on the other hand the saying is actually nothing more than a tautology. The rest mass of a body is simply the mass measured by an inertial frame at rest with this body.

    By the way, elementary particles, which are allegedly the source of rest mass are seldom at rest.
    Last edited: Jul 7, 2010
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook