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B What does a body "emits" when falling down?

  1. May 7, 2018 #1
    I explain it better. If we bring an electron from higher to lower energy level, the energy gap will be emitted as electromagnetic wave, because of the conservation of energy. When the same situation applies for a physical body, for example letting if falling down from some height, what does it emit while losing its energy?

    My answer would be: it it just emits what it received to increase its energy. Namely the electron was excited by a wave, so it emits wave by losing energy.
  2. jcsd
  3. May 7, 2018 #2


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    Staff: Mentor

    Nothing. The energy simply gets converted from potential energy to kinetic energy.

    What if the atom was excited by a collision with another atom?
  4. May 7, 2018 #3


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    I can see why it could appear to be inconsistent but the two cases you are comparing are significantly different. When you drop a hammer, it gains KE but then converts this KE when it actually hits the ground and the overall effect is that the energy goes into vibrations and heat. For an electron, what happens during the change in its energy level is not knowable because it's a Quantum Mechanical process, the emerging energy (the photon) is all we know about.
    You can accelerate an electron over a high voltage gap (an electron gun in a CRT) and the electron then has identifiable Kinetic Energy which can do damage when it arrives at an object.
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