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I Why were momemtum, kinetic energy and work introduced?

  1. Mar 4, 2016 #1
    why were quantities like momentum, force , potential energy, kinetic energy,work ,etc needed to be introduced in physics?
    and why were they defined the way they are defined?.
    would it not be possible to explain nature without defining these quantities or by using alternate physical quantities ?
     
    Last edited: Mar 4, 2016
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  3. Mar 4, 2016 #2

    Drakkith

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    Even if it is possible, it would be MUCH more difficult. I doubt it would even be possible, really.
     
  4. Mar 5, 2016 #3
    why were quantities like momentum, force , potential energy, kinetic energy,work ,etc needed to be introduced in physics?
     
  5. Mar 5, 2016 #4

    Drakkith

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    I'd say that they relate different quantities to one another in a way that makes it possible to accurately predict a wide range of phenomena. I really don't know how to explain it very well. Without all of those concepts, physics as we know it would be much more difficult, if not impossible. Maybe someone else can explain it better. @Orodruin, any idea?
     
  6. Mar 5, 2016 #5

    A.T.

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    The quantities were defined based on what is useful to make quantitative predictions. For example, a quantity that is conserved over time is useful to predict what will happen.
     
  7. Mar 5, 2016 #6

    Orodruin

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    It was "needed" as it was useful for describing how the world behaves, just as everything else in empirical sciences.
     
  8. Mar 5, 2016 #7

    vanhees71

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    These quantities were introduced into physics because they are very useful to describe nature. From a modern point of view you can ask, whether you need forces, but all other quantities (i.e., momentum, energy, angular momentum) are related to the most fundamental properties of our description of nature, i.e., the symmetries of Newtonian and special-relativistic spacetime. These symmetries explain a lot why the physical laws the physicists discovered over the centuries look as they do. The most fundamental discovery is the discovery of these fundemental symmetries.
     
  9. Mar 5, 2016 #8
    I'll try to answer this question in the chronology of which we study these topics. Before the time of Galileo and Newton most of the ideas about the motion of bodies were quite crude. It was Newton who first gave proper mathematical laws for the motion of bodies. His laws make use of concepts such as velocity (if we're studying motion then what better way to express it than change in position with time?), acceleration and forces ( which basically is the cause of motion or how motion is transferred b/w bodies). This was all well when we are doing problems of kinematics and simple dynamics, but then for problems such as collisions and variable mass systems, the idea of momentum and impulse was needed. Also, there were a different class of situations where the forces varied with distance instead of time, here the ideas of work and energy come into the picture. Some of these quantities, such as momentum and energy, turned out to be quite fundamental and also followed conversation laws.
    These concepts are tools used to study the world around us. Why specifically these quantities? Because they seem to work best for us. Many concepts have been dropped in the past because they weren't satisfactory and in the future we probably will get some new quantities which lead to better understanding of nature.
     
  10. Mar 5, 2016 #9
    a new quantity was defined for rate of change of velocity, momentum,work,etc but no special name for rate of change of acceleration .
    was it because rate of change of velocity, momentum,work, occurred frequently in equations ,hence for simplification?
     
  11. Mar 5, 2016 #10

    Drakkith

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  12. Mar 5, 2016 #11
    alright aim of my ques was different. if consider second derivative of momentum?
    a new quantity was defined for rate of change of velocity, momentum,work,etc but no special name for second derivative of linear momentum .
    was it because rate of change of velocity, momentum,work, occurred frequently in equations ,hence for simplification?
     
  13. Mar 5, 2016 #12

    Drakkith

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    Pretty much. Those quantities which are used the most are the ones which have names assigned to them.
     
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