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Homework Help: Coefficient of friction of a sitting block

  1. Oct 22, 2008 #1
    1. The problem statement, all variables and given/known data
    Imagine a block sitting on an inclined plane rather than a flat surface. The angle Ө made by the plane relative to the horizontal can be changed. We could determine the coefficient of kinetic friction by inclining the plane (increasing Ө) until the block slides at a constant velocity once started with a small push. Derive the expected relationship between the angle at which this happens and the coefficient of friction.

    3. The attempt at a solution
    My understand of physics is very slim. However, from what I believe, as the the angle increases, the coefficient of friction will also increase. I'm not even sure if this is what the question is even asking...

    Please, help.
  2. jcsd
  3. Oct 22, 2008 #2


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    Homework Helper

    Welcome to PF.

    Not exactly.

    The coefficient of friction remains the same. What changes is the normal force that translates to frictional force - it lessens.

    At the same time the gravitational pull down the incline increases from 0 when level. Decreasing normal force and increasing sideways force guarantees that it slips down the slope unless it is nailed to the incline.
  4. Oct 22, 2008 #3
    Thank you for replying so quickly! I love this site already .. hehe

    Anyhow! I think I understand what you are saying. Basically, The coefficient of friction of the block stays the same, but as the block is tilted sideways, gravity will continue to pull the block down which changes the normal force and decreases the frictional force.
  5. Nov 10, 2008 #4
    I recently did an experiment on 'Coefficient of Friction' where there is a block which has a wooden surface... The examiner asked to write a report on the experiment on the following things-
    a) Factors that may change 'Coefficient of Friction'
    b) If there is a change in the angle of the inclined plane, what will happen to the 'Coefficient of Friction' ?
    c) What will happen to the 'Coefficient of Friction' when you add masses ?
    d) Compare the horizontal and inclined plane results...
    I have to submit this report by tomorrow, can someone please take some time out and help me write out the answers to the above questions ?
  6. Nov 11, 2008 #5


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    What factors do you think enter into frictional forces?

    Here is a start from Wikipedia:
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