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Difference between momentum and linear inertia

  1. Apr 7, 2016 #1
    Hi everyone, I have always been confused by momentum and linear inertia. What exactly is the difference between them? Aren't them both resistance to change in motion? Its hard to explain what I am confused with so heres an example: if there are 2 moving cars travelling at the same speed and car A has a greater mass than car B, why would it be more difficult to stop car A than car B? Is it because car A has greater inertia or is it because car A has greater momentum? I cant distinguish between them two. Could someone please help me? and please explain why it is one but not the other.
    Thank you so much!
     
    Last edited by a moderator: Apr 7, 2016
  2. jcsd
  3. Apr 7, 2016 #2

    PeroK

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    I must admit I never use the word "inertia". Inertia is simply mass by another name. It's not momentum anyway.
     
  4. Apr 7, 2016 #3
    But whats the difference between the two? Thank youu
     
  5. Apr 7, 2016 #4

    PeroK

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    You mean the difference between mass and momentum?
     
  6. Apr 7, 2016 #5
    I meant the difference between linear inertia and momentum. I thought linear inertia does exist though? and it's different from mass?? Please correct me if I am wrong I am really confused by linear inertia, momentum and mass...
     
  7. Apr 7, 2016 #6

    PeroK

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    Well, if I've got to where I am and never heard of "linear inertia", it can't be very important! I suspect it's a fancy phrase for ... mass!
     
  8. Apr 7, 2016 #7
    I see... thank you for helping :)
     
  9. Apr 7, 2016 #8

    sophiecentaur

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    Inertia is never defined in text books of basic mechanics so I am reluctant to use it or to have much of an opinion about it - other than it is often used instead of 'mass', but to sound more meaningful for some people.
    Momentum is certainly not a 'reluctance to change Momentum but Mass could be though of as a reluctance to change momentum (In Newton's Laws of Motion - somewhere?)
     
  10. Apr 7, 2016 #9

    mathman

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    Above from wikipedia
     
  11. Apr 7, 2016 #10

    sophiecentaur

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    The clue, here, is the phrase "In common usage". Physics terms are physics terms and common usage frequently gets it hideously wrong. By 'wrong' I mean that the terms do not follow consistent rules when 'used commonly' and cause confusion. This is an example where Wiki gets mixed with Dictionary definitions. Mostly, Wiki does better.
     
  12. Apr 7, 2016 #11

    FactChecker

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    An object can have a lot of inertia even if it is not moving at all. It would resist any force to accelerate it. But it would have no momentum.
     
  13. Apr 7, 2016 #12

    sophiecentaur

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    Can you give a definition, which could be used in an equation of motion, for instance? What could be done to measure the inertia that the object you are quoting actually has? Without that, inertia is not a quantity that can be used, validly, in Physics.
     
  14. Apr 7, 2016 #13

    sophiecentaur

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    Sounds to me like the tail wagging the dog.
    We spent hundreds of years trying quite successfully to formalise our Science. What, then, is the point of trying to slot into that structure, a word that just doesn't fit? Who benefits from that?
    If this were a creative writing forum, then I would be all in favour but PF is supposed to be a PF.
     
  15. Apr 7, 2016 #14

    FactChecker

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    Ok. I'll buy that.
     
  16. Apr 7, 2016 #15
    So, inertia does not exist as a physics term? It is mass that I am supposed to be concerning? and please correct me if I am wrong: mass is a resistance to acceleration and momentum is the tendency for an object to keep moving. If this is correct then what is the difference between mass and momentum? thank you
     
  17. Apr 8, 2016 #16

    A.T.

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    Look at their precise mathematical definitions, instead of hand wavy descriptions.
     
  18. Apr 8, 2016 #17

    sophiecentaur

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    Why not look up the definition, rather than waving your hands about? Momentum is one of the very fundamental quantities in Physics and it is defined Exactly.
     
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