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I No Potential Energy due to Sphere of Mass?

  1. Oct 10, 2016 #1
    So we all know that it takes work to build up a sphere of charge by taking charge from infinity and piling it up into a sphere. Since the sphere wants to break apart under repulsion, its like a spring. It has intrinsic potential energy.


    However it doesn't seem the case with a sphere of mass, with no charge. It takes energy to disassemble it. But no energy to build it, since it happens naturally under gravity.

    What does this all mean? Does this mean that in the classical sense, constructs of mass has no energy?
     
    Last edited: Oct 10, 2016
  2. jcsd
  3. Oct 10, 2016 #2
    Masses only attract, there is no repulsion in Gravity.
     
  4. Oct 10, 2016 #3
    Does that explain why clumps of masses exists and clumps of charge doesn't?
     
  5. Oct 10, 2016 #4
    No
     
  6. Oct 10, 2016 #5
    But masses will clump up naturally due to gravity. Solid electric spheres of same charges needs external something to stablize it. But mass doesn't.
     
  7. Oct 10, 2016 #6
    What is the diameter of your 'solid' sheers?
     
  8. Oct 10, 2016 #7
    Lets just say large enough so that you don't have to go quantum or relativistic.
     
  9. Oct 10, 2016 #8
    Mmmm....you are describing where not to go......what about 100mm diameter. Have you come across such a solid electric charge?
     
  10. Oct 10, 2016 #9
    No i have not.
     
  11. Oct 10, 2016 #10
    Well I have a 100mm diameter hemisphere in front of me that needs charging.
     
  12. Oct 10, 2016 #11
    Oh I get it. So you just need to induce a potential difference and clumps of charge will form in a conductor. And this can occur naturally.

    Is the energy put in to create the potential difference form a clump of charge Q a conductor the same as the potential energy of a solid continuous sphere of charge Q?
     
  13. Oct 10, 2016 #12
    My hemisphere relies on gravitational potential difference to form a clump.
    What do you mean by a 'continuous' sphere of charge?.... Charge consists (as far as I know) of discrete entities (1.6x 10^-19).... Not a continuum.
     
  14. Oct 10, 2016 #13
    I'm talking about classical electrostatics where there can be charges that are continuous. Besides, aren't electrons so small that they can be considered as differentials? e.g dq.
     
  15. Oct 10, 2016 #14
    You are confused about discrete and continuous !! Earlier you refer to 'clumps' of charge in my hemispherical Container And now you are using classical ideas to refer to continuous Charges. You cannot mix up 'discrete' (quantum) ideas with 'continuous' (classical) ideas easily.
    'Differentials' are a mathematical idea as are 'integrals'
     
  16. Oct 10, 2016 #15
    I know that continuous charges do not literally exist. But if I take a trillions of electrons and put them together, would it not have a net charge that is numerically similar to one that is evaluated with integrals?
     
  17. Oct 10, 2016 #16
    You have forgotten your original question.
    The answer I gave is that masses do not repel.....has your original question been answered? How will your current question help you get to grips with your original question?... Are you any wiser?
     
  18. Oct 10, 2016 #17
    Energy is released during the process (exactly the same amount it would take to disassemble it later). For example a third of the heat coming out from Earth core is primordial heat left over from the times of Earth formation. This is also how stars ignite.
    Objects closer to the gravitating mass have less potential energy that those further away. By convention potential energy is assumed to be 0 for objects 'at infinity'. This makes gravitation potential energy negative everywhere. Thus the notion of gravity well we live in.
    But for practical purposes you can place the origin anywhere you like.You you set 0 to be at sea level, objects above it will have positive energy, below it - negative.
     
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