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Preservation of kinetic energy

  1. Jan 4, 2010 #1
    Does preservation of kinetic energy of some body after collision(elastic for example) determine preserving of its mass?Is complete preservation of kinetic energy of two bodies after collision even possible?
  2. jcsd
  3. Jan 4, 2010 #2


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    What kind of body - and what kind of kinetic energies?

    If one is talking of high energy particles, as sufficient energies, new particles can be created by transforming energ into matter.

    If one is discussing nuclear particles like neutrons or subatomic particles interacting the nuclei the mass may increase, decrease or remain the same depending on the type of nuclear reaction involved. If a neutron is absorbed, the resulting radionuclide may emit a gamma ray on the order keV or MeV. That is the equivalent of mass loss. One would need to consider if the reaction is endothermic or exothermic. Of course the neutron could scatter elastically.

    In more classical (everyday cases) where KE < rest energy/mass, the mass is preserved regardless of whether the collision is elastic or inelastic.

    "An elastic collision is defined as one in which both conservation of momentum and conservation of kinetic energy are observed."

    "Macroscopic collisions are generally inelastic and do not conserve kinetic energy, though of course the total energy is conserved."

    In general, when bodies of matter (atoms) collide, energy is dissipated in the form of friction, heat (thermal energy), sound (acoustic energy) and mechanical deformation.
    Last edited: Jan 4, 2010
  4. Jan 4, 2010 #3
    Thank You for answer.I can see now that what I really want to know is if kinetic energy of each particle may stay the same after collision.If during collision some energy is created in diffrent forms (like heat,sound etc),and mass stays the same it must come from kinetic energy of particles befor collision.Am I wrong? My questions comes from reading about elastic scattering which is part of topic I try to learn about(center of the galactic).
    If its not a place I should ask such questions please let me know (and redirect me somwhere if you dont mind).Also I realize some parts of my questions may be trivial or simply childish but last time I had a physics lesson at school was 20 years ago ( highschool in Poland) :-)).Thanx again . Matt
    Last edited: Jan 4, 2010
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