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Impulse is change in momentum

  1. Dec 13, 2009 #1
    Hello!
    yes is from Sweden and my English is not good, but will try to do as best as possible. My question is:
    why can not consider the momentum as the acceleration energy?

    I know that:
    Impulse is change in momentum which is not the same as energy
    Impulse can be expressed either as F * (delta) t or m * (delta) v since it is the same thing. That the expressions are as follows from Newton's 2nd Kraftlag together with the definition of acceleration: (delta) v / (delta) t

    but as we move into the energy we see that energy is defined as:
    W = mv ^ 2 / 2

    if we compare the energy between, thus förendringen Middle two speeds we get that the change in energy is:
    http://www.pluggakuten.se/wiki/image...itled11111.jpg [Broken]
    I can not see a big difference between them, the only thing that separates them is that we have abbreviated removed (delta)stretch

    but what is the difference between rörelsenergi and momentum:

    I couple of things:
    An important difference is that momentum is always kept in a collision between two or more objects. The kinetic energy conservation is generally not in a collision.
    Another difference between kinetic energy and momentum is that kinetic energy is a scalar (ie, has size but not direction) while the momentum is a vector (ie, both the size and direction)

    but I can not really understand what the difference between momentum and kinetic energy (accelerating energy)
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Dec 13, 2009 #2
    Re: momentum

    Hello!
    yes is from Sweden and my English is not good, but will try to do as best as possible. My question is:
    why can not consider the momentum as the acceleration energy?

    I know that:
    Impulse is change in momentum which is not the same as energy
    Impulse can be expressed either as [tex] F \cdot \Delta t[/tex] or m * (delta) v since it is the same thing. That the expressions are as follows from Newton's 2nd Kraftlag together with the definition of acceleration: (delta) v / (delta) t

    but as we move into the energy we see that energy is defined as:
    W = mv ^ 2 / 2 [tex] mv ^ 2 / 2[/tex]

    if we compare the energy between, thus förendringen Middle two speeds we get that the change in energy is:
    http://www.pluggakuten.se/wiki/image...itled11111.jpg [Broken]
    I can not see a big difference between them, the only thing that separates them is that we have abbreviated removed (delta)stretch

    but what is the difference between rörelsenergi and momentum:

    I couple of things:
    An important difference is that momentum is always kept in a collision between two or more objects. The kinetic energy conservation is generally not in a collision.
    Another difference between kinetic energy and momentum is that kinetic energy is a scalar (ie, has size but not direction) while the momentum is a vector (ie, both the size and direction)

    but I can not really understand what the difference between momentum and kinetic energy (accelerating energy)
     
    Last edited by a moderator: May 4, 2017
  4. Dec 13, 2009 #3
    Re: momentum

    Hello!
    yes is from Sweden and my English is not good, but will try to do as best as possible. My question is:
    why can not consider the momentum as the acceleration energy?

    I know that:
    Impulse is change in momentum which is not the same as energy
    Impulse can be expressed either as F * (delta) t or m * (delta) v since it is the same thing. That the expressions are as follows from Newton's 2nd Kraftlag together with the definition of acceleration: (delta) v / (delta) t

    but as we move into the energy we see that energy is defined as:
    W = mv ^ 2 / 2

    if we compare the energy between, thus förendringen Middle two speeds we get that the change in energy is:
    http://www.pluggakuten.se/wiki/image...itled11111.jpg [Broken]
    I can not see a big difference between them, the only thing that separates them is that we have abbreviated removed (delta)stretch

    but what is the difference between rörelsenergi and momentum:

    I couple of things:
    An important difference is that momentum is always kept in a collision between two or more objects. The kinetic energy conservation is generally not in a collision.
    Another difference between kinetic energy and momentum is that kinetic energy is a scalar (ie, has size but not direction) while the momentum is a vector (ie, both the size and direction)

    but I can not really understand what the difference between momentum and kinetic energy (accelerating energy)[/QUOTE]

     
    Last edited by a moderator: May 4, 2017
  5. Dec 13, 2009 #4

    tiny-tim

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    Welcome to PF!

    Hello! Hello! Hello! Welcome to PF! :wink:

    I'm not sure what you mean by "acceleration energy" or "rörelsenergi", and your link isn't working, but anyway …

    From the chain rule, d(mv)/dt = d(mv)/ds ds/dt = d(mv)/ds v = d(1/2 mv2)/ds.

    Does that help? :smile:
     
  6. Dec 14, 2009 #5
    Re: Welcome to PF!

    In order to acceleration, there must be a job. that is what I call the acceleration energy thus acceleration work. acceleration of work is [tex]F\cdot \Delta s[/tex] and this means increasing the kinetic energy. therefore increases speed.

    what would be linked are:
    http://img195.imageshack.us/img195/4176/40958030.jpg [Broken]



    what I can not understand the difference between kinetic energy and momentum is not so great. we have only shortened away [tex] \Delta s[/tex][/QUOTE]
     
    Last edited by a moderator: May 4, 2017
  7. Dec 14, 2009 #6
    Re: momentum

    This link shows how I have been derived momentum and nothing else-:
    http://img195.imageshack.us/img195/4176/40958030.jpg [Broken]
     
    Last edited by a moderator: May 4, 2017
  8. Dec 14, 2009 #7

    tiny-tim

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    Hi aloshi! :smile:

    (have a delta: ∆ and try using the X2 tag just above the Reply box :wink:)

    Yes, I can see your link now.

    I'll rewrite it so that it's easier to read …

    If we have a very small increase in speed, from v to v + ∆v,

    then ∆KE = 1/2 m ((v + ∆v)2 - v2) = mv ∆v = m ∆s/∆t ∆v = m ∆s (m∆v/∆t) = ∆s F,

    which is the standard work-energy theorem, change in KE = work done by force F moving through distance s.

    (I've used Newton's second law : impulse = force x time = change of momentum, or F ∆t = ∆(mv))​

    After that, I don't follow what your objection is. :confused:

    Are you confusing impulse with work done ?

    Impulse = force x time, but work done = force x distance. :smile:

    Are you saying that for a very small change, distance is proportional to time, and so impulse is proportional to work done? If so, that ignores the fact that, if there is acceleration, distance is never proportional to time (except in circular motion, in which case the work done and the change in KE are zero).
     
  9. Dec 14, 2009 #8
    Re: momentum

    i can't understand what is the difference between Newton's second law and the momentum?
     
  10. Dec 14, 2009 #9

    tiny-tim

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    Newton's second law : impulse = force x time = change in momentum :smile:

    (or force = rate of change of momentum).

    What is worrying you about that? :confused:
     
  11. Dec 14, 2009 #10
    Re: momentum

    I can not understand the properties of momentum has. what is momentum?
     
  12. Dec 14, 2009 #11

    tiny-tim

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    Momentum is mass times velocity.

    It is the derivative of kinetic energy … mv = d/dt (1/2 mv2) :smile:
     
  13. Dec 14, 2009 #12
    Re: momentum

    what is the difference physically, I understand the difference mathematical
     
  14. Dec 14, 2009 #13

    tiny-tim

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    momentum equals available "oomph"

    Momentum is always conserved in collisions (while kinetic energy is not),

    so momentum measures the "oomph" available when something hits something else. :smile:
     
  15. Dec 14, 2009 #14
    Re: momentum

    I could not be pushed to the last:

    "So the momentum measures the" oomph "available when something hits something else"
    can you explain thanks
     
  16. Dec 14, 2009 #15

    tiny-tim

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    Momentum is a quantity which an object has when it moves.

    It can transfer that quantity to another object.

    That quantity is never lost, it only moves from one object to another.

    It measures the ability to move another object …

    the more momentum you have, the more you can move something else …

    the less you have, the less you can move something else …

    if you do move something else, you must give up some of your own momentum. :smile:
     
  17. Dec 14, 2009 #16
    Re: momentum

    Requires no energy to give over part of their own speed?
     
  18. Dec 14, 2009 #17

    tiny-tim

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    Change of energy is not required …

    if you bounce a ball off a wall, there is no change of energy, but the ball exerts an impulse on the wall …

    if the wall is on wheels, it will move, with little or no change in the energy of the ball. :wink:

    What moves the wall is the change in momentum: the change in energy is irrelevant. :smile:
     
  19. Dec 14, 2009 #18
    Re: momentum

    if we are dragging a ball from a height H. After the nozzles have the floor, it will not reach to the height H, but it will not be as high. it mean that we have lost energy?

    if we are dragging a ball from a height H. After the nozzles have the floor, it will not reach to the height H, but it will not be as high. it does not mean that we have lost energy?
    it can not mean that the floor gave a speed, and therefore its momentum. floor can not get a speed
     
  20. Dec 14, 2009 #19

    tiny-tim

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    Yes, if we drop :wink: a ball from a height H (sorry, i have no idea what you mean by "nozzles" :redface:), it will not quite return to height H because of the small amount of thermal energy (heat) generated.

    But that energy creates heat (and/or vibration and noise), not movement.
    No, the floor does get a speed …

    the floor is fixed to the Earth, and when the ball bounces up, the whole Earth moves very very very slightly down! :smile:
     
  21. Dec 15, 2009 #20
    Re: momentum

    there are other ways of thinking that momentum? I want to understand it to 100%
     
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