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Stupid question

  1. Oct 23, 2007 #1
    People say gravity is an extremely weak force. Weaker than any of the other three basic forces that govern our universe. Explanations to this have varied in all forms of radical ideas (I'm not saying I outright reject them). But it has always pestered me the idea that perhaps gravity is such a weak force because matter is mostly compiled of empty space. In a hydrogen atom, if the proton were the size of a pixel on your screen, the electron would be about another 50,000 pixels away most of the time.....right?. Now imagine if all of that empty space had been compacted with protons. The measure of force relative to density is roughly 5.2 x 10^14 times the magnitude of the original force.

    Perhaps I'm missing a concept with my idea here. Mind you I am a physics enthusiast and some of the more advanced topics I am still ignorant to. But I still have the right to ask questions. I hope :smile:

    Your ideas, comments, criticisms, or corrections would be much appreciated. :)
     
  2. jcsd
  3. Oct 23, 2007 #2

    malawi_glenn

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    look at the forces on an electron, which is not made up of anything else than itself (not as in the case of atoms, where you have 99.999..% nothing). Compare the Coloumb force between two electrons separated 1m and the force of gravity betweem them.

    should be a straightforward calculation example for you and it is very illuminating =)
     
  4. Oct 23, 2007 #3

    blechman

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    The gravitational force would be larger in your example, BosonJaw, but think about how much much much much MUCH larger the Coulomb force would be (protons have charge)!

    But you bring up a very good point: gravity is not weak in the world. After all, we are glued to the Earth, galaxies are held together by gravitational binding energy, black holes have an incredible amount of energy to them, etc. The key point in all of this is that there is no "anti-gravity" but there is "anti-electricity" - that is, charges can cancel but masses will always add up. Therefore on the large scale, gravity is quite strong. But that's only because matter is neutral (same number of electrons as protons) so the even stronger Coulomb force cancels while gravity grows.

    Otherwise, the world would look very different! :-)
     
  5. Oct 24, 2007 #4
    Well , the gravity force is the weakest of all, but there is a very important property of gravity: it can accumulate while , let say, electrical force can not. As a result, you can not accumulate a bunch made of only negative (or positive) charged particle, while as for gravity you can, "the more, the better", even to an extent of a galaxy or the like.
     
  6. Oct 24, 2007 #5

    malawi_glenn

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    That just follows from blechman's post, that there are no anti-gravity.
     
  7. Oct 24, 2007 #6
    Different range, different level. If you regard the galaxy as a particle, the gravity is strong. Only on the large scale the gravity will show his power.
     
  8. Oct 24, 2007 #7

    malawi_glenn

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    but if we instead imagined that each atom in a galaxy did not have any electrons, and in another, only the electrons where there; then the electronic interaction would be much much greater ;)

    The reason for gravity to dominate over larger distances is due to the over-all neutrality of matter of large objects, since there exists two types of electric charges. So yes in reality gravity dominates over large distances, but still it is a very very weak force.
     
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