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B Loss of mass

  1. Mar 26, 2016 #1
    Lets say a heavy object was resting on earth and suddently it lost allot of mass.
    Will the object go up? (The loss of mass happened instantly )
  2. jcsd
  3. Mar 26, 2016 #2
    If the object was being compressed by it's own weight (like a spring, the top would be compressing the lower coils) if that weight was instantly reduced the spring would expand away from the Earth as the potential energy is released from the spring.
  4. Mar 26, 2016 #3


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    On the other hand, if you simply mean an object, of mass M, sitting on the ground, reducing the mass of the object, the force of the object on the ground would be reduced but so would the force of the ground on the mass. The reduced mass would still sit on the ground, not moving.
  5. Mar 26, 2016 #4
    However, regardless of whether or not the object is rigid or is elastic, there is no known mechanism which could cause a spontaneous loss of mass.
    (Except perhaps a really tiny loss of mass over a long time if the object is radioactive and losing mass as some form of radiation.)
  6. Mar 27, 2016 #5
    Let me rephrase the question in form of a problem.

    A cube of mass 2t was sitting on some surface on earth (so there is a force pulling it towards the center of the earth)

    Using the 2nd law of newton the earth would be pulling the objet with a force of 20kN.

    And using the 3rd law of newton the support would push the object with the same force.

    If the mass of this cubic object changed to 1 kg instantly keeping the same volum.

    Wouldn't the surface act as a spring at a molecular lvl and push the opject up and giving it velocity?

    I understand that a suddent loss of mass cant happen but in theory what would happen?
  7. Mar 27, 2016 #6


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    Staff: Mentor

    What do the laws of physics predict if we violate the laws of physics?
    That question does not have a meaningful answer.

    If you put a two ton object on top of something with a mass of 1 kg, and rapidly lift the two ton object up, the 1 kg object below can jump up a bit, because the compressed floor and object will relax, pushing the object upwards.
  8. Mar 27, 2016 #7


    Staff: Mentor

    As has been pointed out, the question is not consistent with the laws of classical physics as we know them, so the question as posed cannot be answered.

    However, what I think you are actually interested in can be answered: if an elastic material is compressed by a given load and if that load is suddenly reduced then the elastic material will decompress.
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