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Why don't two objects bump into each other because of this gravity?

  1. Sep 27, 2012 #1
    Why don't two objects bump into each other because of this gravity??



    We know that, every object which has mass attracts every other object which has mass too. Now, why don't two objects certainly fall into each other? For instance any two stars or even any two objects which are not of that cosmic scale.like two chairs of different masses etc.


    I'm very confused!! :confused:
     
    Last edited: Sep 27, 2012
  2. jcsd
  3. Sep 27, 2012 #2

    phinds

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    Re: Why don't two objects bump into each other because of this gravity??

    They DO, if there are no other forces acting on them.

    If you put two chair in intergalactic space, fairly close together, they will likely fall into each other.
    I have no idea what you are talking about
     
  4. Sep 27, 2012 #3
    Re: Why don't two objects bump into each other because of this gravity??

    But those other forces should act in opposite directions. Right?
    What I suppose is the force of gravity is so weak that any object not very massive does not bump into any other object which doesn't have very large mass. Is this approach correct?
    And yeah ignore the last part.
     
  5. Sep 27, 2012 #4

    ehild

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    Re: Why don't two objects bump into each other because of this gravity??


    Two free objects initially in rest relative to each other do fall towards each other and they will bump into each other. A stone dropped from a tower falls vertically down towards the centre of Earth (and at the same time the Earth falls towards the stone). A stone thrown will follow a parabolic path, and falls to the Earth some distance farther. If you throw the stone so fast that its trajectory reaches beyond the surface of Earth it never will fall down, but becomes a satellite of Earth.
    The Moon falls towards the Earth but at the same time it travels with a certain velocity and the result is a nearly circular orbit.
    Read:
    http://csep10.phys.utk.edu/astr161/lect/history/newtongrav.html

    There can be other forces which act against the force of gravity. It is normal force if an object is supported on a surface (as a book on a table) or friction between two chairs standing on the floor.

    The objects move according to the resultant of the forces and their initial velocity.


    ehild
     
    Last edited: Sep 27, 2012
  6. Sep 27, 2012 #5

    phinds

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    Re: Why don't two objects bump into each other because of this gravity??

    No, it is not correct. The forces DO act in opposite directions. Each chair is pulled towards the other chair. The only question is whether there are OTHER forces keeping them from falling into each other.
     
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