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I Source of Energy in a Field of Forces

  1. Aug 31, 2018 #1
    good evening!

    My question is the following: it is well stated that energy is conserved in any isolated system, and we can in most circumstances expand our system to a many-steps conversion of energy, but always conserved. The classic example could be the energy of the sun stored in form of chemical energy in the plants, which are eaten by a man that converts such an energy into motion when he pushes a ball, and so on.

    But when we consider fields of forces, who is the source of the energy they give to things (like an object who gains energy from the gravitational field as it gets near to the earth)?

  2. jcsd
  3. Aug 31, 2018 #2


    Staff: Mentor

    The field itself. The field has an energy density which is reduced.
  4. Aug 31, 2018 #3


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    Homework Helper

    An object in Earth's gravitational field has potential energy. When that object falls from a height to the ground, (some of) that potential energy is converted to kinetic energy.
  5. Aug 31, 2018 #4


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    Staff: Mentor

    Note also that energy is conserved. Drop a rock and it gains kinetic energy vs earth. pick it back up and you give it back as potential energy. And there is no continuous expenditure of energy involved.
  6. Sep 3, 2018 #5
    Could you explain that in more detail, please? I haven’t found a good material on the matter.
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