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Concept Of Linear Momentum and definition of Force

  1. Jun 23, 2012 #1
    I understood that Newton has introduced a concept called "Force" which is basically a cause for an effect i.e. if an object is in a state of rest and if applied a "force" then the object moves (change in velocity, ∴ accelerates) also if an object moves with a constant velocity and is disturbed then an acceleration is produced for the same reason as above. Thus a force is a cause and a change in velocity is an effect. This, based upon my understanding, is deduced from the law of inertia (given by Galileo and simply restated by Newton)!

    What I don't follow is that:-

    2) Why is momentum expressed as mass TIMES velocity?

    3) How did Newton obtain the second law from the momentum concept?

    Please can anyone give examples and explain the momentum concept?
  2. jcsd
  3. Jun 24, 2012 #2


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    Staff: Mentor

    Momentum is a property of motion that is conserved during interactions of free bodies. This fact allows us to calculate velocity vectors after colliding bodies separate, based on their masses and velocity vectors prior to collision^. During most such collisions kinetic energy is not conserved; so it's handy that momentun is.

    ^or viceversa
  4. Jun 25, 2012 #3
    I would say that a push is a cause of a velocity change. A pull works just as well.

    One thing that linear momentum is, is a number that describes a push. If you measure the duration of a push and the force of the push, and multiply those, you get the linear momentum.

    Mass times velocity is an useful number to know, we have named it momentum.

    I have no idea
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