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Mass speed molecular stability

  1. Jul 30, 2011 #1
    If you increase mass with speed does the forces that hold molecules’ together increase in per portion ? If not do the molecules’ fall apart with speed ? If the forces increase in per portion Why does the energy released from the muluation of those forces decrease with speed.
     
    Last edited: Jul 30, 2011
  2. jcsd
  3. Aug 1, 2011 #2
    To a good first approximation, molecular binding forces can be treated as harmonic, just like springs. For such a case, the force is proportional to the displacement. If you heat up a material, the molecules move faster, are displaced more from their equilibrium point and therefore the binding force increases when the molecules are furthest apart. It's not that the molecules are smart and constantly change their force to stay intact. It's just that the force depends on position, and the position changes more for higher speeds.

    But there is a breaking point. At a certain point, the bond is just not strong enough to withstand high enough speeds. Such points are known as phase change points (melting point, boiling point, etc). Heat water hot enough and the water molecules speed up beyond what the bonds can hold and break apart and form steam.

    You last question contains many misconceptions. First, energy is not released when you break chemical bonds. It is the opposite. It takes energy to break bonds. Think of trying to smash glass to separate bits with a hammer, or of trying to get apart two dancers who are tightly bonded. You have to apply energy to break bonds. Second, the energy required to break a molecular bond does not depend on speed, it only depends on the bond energy which is determined by the quantum mechanical specifics of the bond. Think of the molecule as sitting in a potential well, and we need a certain amount of energy to lift it up out of the well.
     
  4. Aug 2, 2011 #3

    Drakkith

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    Staff: Mentor

    Just to clarify, are you thinking that accelerating an object to a high velocity increases its mass? If so, that is incorrect.
     
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