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Kinetic friction in a two mass, one pulley problem

  1. Feb 2, 2016 #1
    1. The problem statement, all variables and given/known data
    I have solved the problem where one mass m1 is on a horizontal frictional table connected to a mass m2 which is hanging off the table by a string over a pulley (assuming pulley massless), assuming that m2 is greater than m1 there is a net acceleration causing the mass 2 to fall down and the mass 1 to follow. The problem is that the equations suggest that an increased pulling force (i.e. larger m2) causes an increased coefficient of kinetic friction, furthermore I apply this formula to the data I have and indeed a larger hanging mass gives a greater kinetic friction coefficient. Is this correct? I would have thought it should not effect the coefficient.

    2. Relevant equations

    3. The attempt at a solution
    Solution already obtained, the question is about the solution.
  2. jcsd
  3. Feb 2, 2016 #2


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    Homework Helper

    If you hold your coefficient constant, what would have to change? Is there another term that might be variable in your equation?
  4. Feb 2, 2016 #3
    the only other variables are m2 and of course the acceleration, but using the data i have for the acceleration which was found using a camera and tracking software, i still find an increasing coefficient of kinetic friction with increasing m2
  5. Feb 2, 2016 #4


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    That is interesting. You have data for the two different masses and the acceleration terms are the same?
    I would recommend running a third test -- maybe with masses that are close to each other -- clearly acceleration will need to change at some point.
  6. Feb 2, 2016 #5
    Coefficient of friction depends on the surface on which the mass under consideration moves/undergoes relative motion
    It has nothing to do with the mass of the body which experiences the frictional force!
  7. Feb 2, 2016 #6
    no, the acceleration does increase with increasing m2, but so does the kinetic friction coefficient. My understanding is that the kinetic friction should be independent of m2 and thus independent of the acceleration but this does not seem to be the case.
  8. Feb 2, 2016 #7
    i agree, but the formula and my data do not seem to suggest this, my question is why
  9. Feb 2, 2016 #8
    Could you provide an actual picture of the data you possess??

  10. Feb 2, 2016 #9
    Here is the data:
    where the paper types are what m1 is being dragged over, and 30,40 and 50g corresponds to mass m2.
  11. Feb 3, 2016 #10
    any more ideas???
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