Maximum coefficient of friction

  1. Can someone explain why the maximum coefficient of friction is 1??

    Why μ <= 1 ???

    Thank You.
  2. jcsd
  3. malty

    malty 161
    Gold Member

    I dunno I thought it could be greater than one . . . :confused:
  4. It could be greater then 1. For example if you have glue, or a really viscose m aterial between the two surface.
  5. But if you are talking about glues and something like this, you are not talking about friction, it's a different force.

    For definition, when the coefficient of friction is m:


    And I wonder, why m<=1?
  6. malty

    malty 161
    Gold Member

    Are you sure this isn't the elastic coefficient you're mixing it up with???
  7. cristo

    cristo 8,387
    Staff Emeritus
    Science Advisor

    No, the coefficient of friction does not need to be less than one. For two surfaces glued together, for example, the coefficient of friction would be infinite.

    You may be confused by the fact that most of the surfaces you will be doing calculations for will have coefficients of friction less than one. This is simply because, in those cases, we are more interested in surfaces that slide relatively well against each other.
  8. You don't need glue. I recently attended a horse pulling contest where the winning team weighed about 3600 lb and pulled about 3900 lb. That's a coefficient of kinetic (yes, their hooves were slipping a little) friction of 1.08. Some other candidates for high coefficients might be a cheese grater, no 40 sandpaper, a file, stainless steel on aluminum, etc.
  9. Thank you everybody.

    Now I understand the coefficient friction can be higher than 1.

    Another explication is that in a ramp, the coefficient of friction is equal to the tangent of ramp's angle.

    The angle can be higher than 45º, so the tangent would be also higher than 1, as a consequence we can get a coefficient as high as we want (considering that a body is holded in the ramp).
  10. rcgldr

    rcgldr 7,704
    Homework Helper

    Top Fuel drag car tires are getting a coefficient of friction well over 4.5. Table Tennis rubber is probably the stickiest, take a look at this video:

  11. When talking about friction, never refer to glues or something like that. Glues adhere by different force,not friction.
    I agree that most of the friction coefficients are lower than 1. There is reason for that. If you magnify the two surfaces of the table and let say an iron bar, these surfaces are not smooth but made of many micro hills (which you can see in an SEM picture of a metal). The steeper the hills (triangles), the higher the friction coefficient. If the steepness is 45 degrees, probably the coe. is 1. For many materials, the hill should not be steeper than 45 degrees, that the reason why coeficients are mainly lower than 1. Anyway, there are exceptional cases.
  12. That's only going to be the case if the Net force is 0 of an object on a ramp.
Know someone interested in this topic? Share this thead via email, Google+, Twitter, or Facebook

Have something to add?