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Frictional force and Normal force

  1. Sep 19, 2013 #1
    when a body is slided or move in a horizontal floor, the Frictional force is directly proportional to the Normal force acting on the body. Is there is any proof (emperically or Theoretically)
     
  2. jcsd
  3. Sep 19, 2013 #2

    arildno

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    Yes. bundles of it, experimentwise.
     
  4. Sep 19, 2013 #3
    It is an empirical relationship
     
  5. Sep 19, 2013 #4

    arildno

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    To be specific, the local frictional force has been establish to be proportional to the local point pressure.

    This point pressure, roughly equals N/A, where N is normal force, A is area, so that the frictional FORCE equals k*(N/A)*A=kN, for k constant of proportionality.
     
  6. Sep 19, 2013 #5

    HallsofIvy

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    In fact, like most simple physics laws, it is a "first order" approximation. Any "reasonable" (analytic) function can be written as a power series, f(x)= a+ bx+ cx^2+ .... Obviously, if there were NO normal force holding object to surface, there is no friction so a= 0. Approximating the function by its linear approximation, f(x)= bx so f is proportional to x to the first order in x.
     
  7. Sep 19, 2013 #6

    rcgldr

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    In the case of tires, there's a load sensitivity factor, reducing the coefficient of friction as the load increases. Wiki artcile, although this is for static friction:

    https://en.wikipedia.org/wiki/Tire_load_sensitivity
     
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