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How does force travel actually?

  1. Aug 10, 2011 #1
    Force is a push or pull. Is it just the transfer of energy from one body to another? If yes, why does it mostly result in the acceleration of the body?
    If no, then how does force travel?
     
  2. jcsd
  3. Aug 10, 2011 #2

    A.T.

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    No, it is the transfer of momentum:
    http://en.wikipedia.org/wiki/Momentum#Relating_to_force_.E2.80.93_General_equations_of_motion

    Net force is defined via the acceleration:
    http://en.wikipedia.org/wiki/Momentum#Relating_to_mass_and_velocity

    The notion that "forces cause acceleration" is a philosophical one. Physics merely states that net force and acceleration are proportional, and the proportionality constant is called mass.

    On a fundamental level disturbances propagate as electromagnetic fields.
     
  4. Aug 10, 2011 #3
    Force is not a property of an object, but instead is an interaction between objects (object A exerts a force on object B and vice versa), so as such it doesn't really travel.
     
  5. Aug 10, 2011 #4
    I didnt exactly understand that how do the objects interact with each other causing acceleration .
     
  6. Aug 10, 2011 #5
    Hi Akash:
    I'm assuming you are asking an introductory question.

    Try reading about FORCE in Wikipedia.

    In general terms you CAN think of a force as transferring energy....sometimes it causes acceleration, sometimes not. For example if I kick a ball, it moves and may go flying some distance; If I kick a brick wall I might deform the wall a tiny bit, but I might also deform my foot by breaking it. In all three cases energy is transfered...in the first it's momentum/acceleration that mostly results, in the latter in the form of heat as I compress the wall or my foot....(Of course you deform the ball briefly as you kick it,too)

    Which I touch something like in the above examples, electrons in my foot repel electrons in the object. That can also happen over distances as in electrical repulsion or attraction force:
    F = Kq1q2/r2

    With such field forces, the force (really the energy) is carried by the electromagnetic field which can be considered particles and or waves....the particle view uses photons as the quanta of the electromagnetic field.....

    There are other force fields as the strong,weak and magnetic as well.

    In some cases it's not obvious just what energy if any is being transferred, as in an electron orbital moving around a nucleus....Our standard equation which I gave above does NOT explain such interactions....
     
  7. Aug 11, 2011 #6
    o..o..ok....thanks
     
  8. Aug 11, 2011 #7
    Not all objects accelerate when a force acts on them. Some slow down, which is negative acceleration, owing to a force that 'opposes' its motion; while (if calculated force is applied) you can also set things up so a force will merely change the direction of the moving object and neither accelerate nor decelerate.

    It's a bad idea to think of force as a transfer of energy between bodies because while it appears so, that is not what actually happens, strictly speaking. As A.T. rightly put it, it is more of a transfer of momentum.
     
  9. Aug 11, 2011 #8

    WannabeNewton

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    [itex]\vec{F} = \frac{\mathrm{d} \vec{p}}{\mathrm{d} t} = -\triangledown V[/itex]. They are not unrelated quantities.
     
  10. Aug 11, 2011 #9
    If you push a trolly, you feel the same force (in the opposite direction) to your push, but the friction of your shoes stops you moving in the opposite direction.

    Think about what happens at the fundemental level between the contact point of your hands with the handle of the trolley.
     
  11. Aug 11, 2011 #10
    I'm not saying they're entirely unrelated.
    Of course the gradient of Potential Energy is directly related to Force; but, while force can be defined in terms of energy, force isn't the transfer of energy per se, rather it is via a transfer of momentum that a form of energy conversion becomes apparent.
     
  12. Aug 11, 2011 #11

    WannabeNewton

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    Yeah sorry I reread your post, I understand the point you are making =D.
     
  13. Aug 11, 2011 #12
    I can state the difference between K.E. and momentum by their definitions, but intuitively to me they are very similar. Someone care to explain the differences in real life situations?
     
  14. Aug 11, 2011 #13
    In this context, to put it simply, KE arises as a result of momentum. Initially, a body has Potential Energy (say) then one applies a force, transfers momentum which, in turn, introduces a KE in the body.
     
  15. Aug 11, 2011 #14
    Force changes the physical state like motion,position,So that it most results in acceleration.It push or pull the object changing the physical states like velocity and displacement and distance.so that it causes some change in velocity in a particular interval of time.That is nothing but Acceleration.
     
    Last edited: Aug 11, 2011
  16. Aug 11, 2011 #15
    One thing to be careful of is that force is only the gradient of some potential energy only if it's a conservative force, so I would leave out the gradient function to avoid confusion. After all, you can have a force that isn't conservative, so thinking of it in terms of momentum is more accurate.
     
  17. Aug 11, 2011 #16

    A.T.

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    The main benefit of those concepts are theirs conservation laws. Since momentum is a vector, while energy a scalar the conservation has quite different implications for both. KE can be converted into some other energy form, but you cannot get rid of the momentum in closed system.
     
  18. Aug 11, 2011 #17
    From all this responses, I think, we can safely say, we do not know what force is. When ball 1 hits ball 2, ball 2 moves. Why does it move? We do not know the reason, but it moves. So, let's call the reason 'Force'. The rest (momentum, acceleration) is the history.

    Yes, it may sound philosophical, but giving something a 'name' doesn't mean we know it or it has been explained. On the contrary, sometimes we hide the 'reason' by giving it a 'name'.
     
    Last edited: Aug 11, 2011
  19. Aug 11, 2011 #18
    If the ball did not move, then the universe would not be like it is.

    In another theoretical universe, it may be the case that an object disappears as soon as you touch it. I think that there is no real "reason" for force... force just is how it is.
     
  20. Aug 11, 2011 #19
    It could be a combination of the absolute identity of electrons, energy conservation, and the fact that two rotations, done in different orders, end up in different places.
     
  21. Aug 12, 2011 #20
    momentum is just the product of mass and velocity.
    But then how is it transferred from one body to another if it is not exactly energy?
     
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