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Homework Help: Lab - Friction and Forces on an Incline

  1. Mar 26, 2009 #1
    Okay, so I am writing a lab but I am quite stuck on one question.

    Using the average force of sliding friction from the data, calculate the coefficient of sliding friction.
    Average force of sliding friction: 0.32N

    The equation I used to calculate other static/sliding coefficients was:
    And X is the value of an angle.

    I am confused because I don't know if I can use this formula to calculate the coefficient because the average force of sliding friction is not an angle.

    If I use the average force of sliding friction as an angle I get:
    (9.8xSin0.32)/(9.8xcos0.32) = 0.006
    This does not seem right, anyone have any ideas?
    please and thanks.
  2. jcsd
  3. Mar 27, 2009 #2


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    Homework Helper

    Don't you want to look to the definition of μk?

    μk = Ff/Fn

    If you have determined Ff, then aren't you just interested in dividing by the Fn ?
  4. Mar 29, 2009 #3
    Okay, thank you, I think I understand.
    What I tried was:
    Would that make sense?
  5. Mar 29, 2009 #4


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    Not quite.

    The normal force is given by cosθ * weight, but there is also the component of gravity down the incline of sinθ * weight. If the force you are measuring pushing up the ramp is .32N then isn't that the result of the relationship that

    .32 N = μ*m*g*cosθ + m*g*sinθ

    If .32N is measured pushing down the ramp then

    .32N = μ*m*g*cosθ - m*g*sinθ
  6. Mar 29, 2009 #5
    Okay I get it!
    thank you so much for the help!
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