Energy is neither created nor destroyed

  1. Excuse me if this question is stupid or naive.

    If there is a body in space, what is the total energy of that body?
    If initially the K.E of that body was zero and then I pushed it in a certain direction .. it will keep moving until it reaches another body that have a certain gravity ( earth for example ) and in this case it has P.E

    but if I pushed it in another direction ( with the same force ) .. it will keep moving until it reaches another body ( sun for example ) and in this case it will gain also P.E but with a different value

    does not that mean that in the second case the amount of total energy was greater ?
     
  2. jcsd
  3. mmmmmm, maybe in the very beginning it's P.E was the summation of all the P.E that it will gain from all objects. am I right ?

    but does not that mean that all objects in the universe have the same P.E ?
     
  4. Your question is really hard to understand but one thing is for sure , if there is a object somewhere and you push it with a force "a" then now it has it's own kinetic energy whatever it was before the push +the "a" or in other words the object gains kinetic energy from the force exerted on it, depending on the force depends the kinetic energy that the object will have .
     
  5. Thanks for your reply, my question is related to the Potential energy.
    If this object is hanging in space and not moving at all. If I pushed it to the left with force "a" it will keep moving in the left direction until it reaches a gravity field of a certain object and in this moment it will gain Potential energy X based on the gravity field of that object

    but if I pushed it to the right (the opposite direction) with the same force "a" it will keep moving in the right direction until it reaches a gravity field of another object and in this moment it will gain Potential energy Y based on the gravity field of that object.

    Does not that mean that Energy was different ?
     
  6. No. The body does not "gain potential energy" suddenly when it approaches another object in its way. It had certain potential energy before you pushed it because the gravity range is infinite. As you push it towards one object, approaching it it will actually be losing the P.E. due to that body because the distance to it is decreasing, but at the same time the distance from the opposite object will be increasing and the P.E due to that object will be increasing, so that the total of energy will stay constant.
     
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