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I Direction of momentum transfer?

  1. Feb 20, 2017 #1
    Does the momentum always get transferred from lower velocity to higher velocity(may be along a negative velocity gradient.)
    Consider the collision between 2 bodies M1 and M2,(M1<M2) but both having the same momentum.So M1 will have a higher velocity than M2(V1>V2). Now if the velocities V1 and V2 are in the same direction and M1 collides with M2 then the momentum of M1 will increase, meaning momentum of M2 will decrease. So the momentum has got transferred from higher velocity body to lower velocity body even though the momentum of both is same.
    Even if the body M2 had the higher momentum than M1 before collision after collision its velocity would still increase.
    So am I correct in assuming momentum gets transferred along negative velocity gradient?
    Ps: This question came to my mind in context of momentum transfer in fluid flow
     
  2. jcsd
  3. Feb 20, 2017 #2

    sophiecentaur

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    Hi and welcome.
    I think you would need to specify the situation better before we can come to any conclusion. Momentum can be 'shared' or 'exchanged', depending on the energy loss in the collision.
     
  4. Feb 21, 2017 #3
    @sophiecentaur Thank you for your reply.
    Let's consider an inelastic collision. I do realise the loss of kinetic energy will be in such a way so as to respect the momentum conservation.
    I am interested in the direction of the momentum transfer. Is there a gradient along which the momentum gets transferred. For example, heat is transferred along temperature gradient even from a low heat content system to a higher heat content system.
     
  5. Feb 21, 2017 #4

    A.T.

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    Momentum is transferred both ways (exchanged) between the bodies (see Newton's 3rd Law)
     
  6. Feb 21, 2017 #5
    @A.T. Thank you for your reply ..
    Yes, I have understood that when both bodies collide, they both have same force applied to each other in form of action and reaction.
    But is the body with higher velocity always reduce its velocity or rebound and have its velocity reversed(again in a way reduced)?
    When we talk about momentum transfer does it have a direction in which it is transferred?

    When u say exchanged it doesn't have a direction as it is both ways. Are the momentum of one body increasing and others decreasing?
     
  7. Feb 21, 2017 #6

    A.T.

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    No, the speed of the initially faster body can sometimes increase, while the speed of the slower body is reduced.
     
  8. Feb 21, 2017 #7

    ZapperZ

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    May I suggest that you check this for yourself here?

    https://phet.colorado.edu/sims/collision-lab/collision-lab_en.html

    Zz.
     
  9. Feb 21, 2017 #8

    sophiecentaur

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    To be honest, I can't be sure what you are looking for. You seem to be after a 'general rule' but I'm not sure there is one, in your terms.
    One approach I could suggest would be to view the collision from the frame of the CM of the two masses. The momentums (momenta?) of the masses will be equal and opposite before and after the collision (total momentum must be zero). If you have an elastic collision, their parting velocity will be equal and opposite to the approach velocity. If totally inelastic, the parting velocity will be zero. That deals with the motion in the CM frame. In the frame of an external observer, you just add the CM velocity to each mass to get what the observer will see.
     
  10. Feb 22, 2017 #9

    A.T.

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    This is the statistical result of many collision between particles. There is no simple rule, of the type you suggest, for all collisions. But some collisions are more likely than others, when a velocity gradient is present among a large amount of particles.
     
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