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Relativistic energy of a ball

  1. Apr 14, 2010 #1
    according to mass-energy equivalent theorem, Regardless of whether the object is at rest or moving, the object of mass m having energy E=mc2.

    suppose a ball of mass m is placed on ground, then how much energy this ball have???
    Is it equal to E=mc2 ??
    now if we place this ball above the ground up to height h, Is this mean all Energy of ball (i.e E=mc2) is converted to potential energy (mgh) ???
    if so this ball have so much tremendous energy!!!!
    how it can be possible?????
  2. jcsd
  3. Apr 14, 2010 #2
    If the ball went up to h all by itself, then yes. Usually ball's don't do that, and the rest energy of a small fraction of its mass would usually blast the ball well above escape velocity if it did.

    Usually the energy to raise the ball h is added by some other force, thus the rest energy of the ball is constant.
  4. Apr 14, 2010 #3
    No, it isn't. But , if the ball is made out of a radioactive material and you let it sit on your desk, it will release an energy:

    [tex]\Delta E=c^2 \Delta m[/tex]

    Now, this can be a tremendous amount of energy due to the huge value of the conversion factor [tex]c^2[/tex]

    If it is radioactive, this is how it is possible. Be careful when you play with radioactive tennis balls :-)
  5. Apr 14, 2010 #4
    mc<sup>2</sup> is descriptive of the isolated ball. mgh is an energy of the ball/earth system. Unfortunately, this potential energy is often said to be part of the ball's energy (e.g. in quantum theory).
  6. Apr 15, 2010 #5
    what is the "descriptive of the isolated ball"?? then does the total energy of the ball contain both quantities i.e (T.E = mc2 + mgh)??
    but in this case the quantitative value of mgh is very much higher than the mc2 in terms of Joule.!!!!!!
    wat is confusion!!!!
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