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Homework Help: Forces on a toppling wheel

  1. Apr 24, 2016 #1
    1. The problem statement, all variables and given/known data
    A stationary bicycle wheel is placed on its rim on rough ground. It topples over. Sketch a free body diagram for the wheel when it is at an arbitrary angle to the vertical and label the forces. Explain qualitatively what happens to the direction and magnitude of each of the forces during the toppling process.
    What I dont get is how the forces change direction and magnitude.
    2. Relevant equations

    3. The attempt at a solution
    What i did was draw the forces like in the picture. Not really sure how they change. I'm thinking at first when theta is small Normal ~ mg. Then friction increases and the normal force decreases.
    Any help greatly appreciated.

    Attached Files:

  2. jcsd
  3. Apr 24, 2016 #2
    Are you sure there is friction? Maybe the normal force changes direction
  4. Apr 24, 2016 #3
    Re thought and the centre of mass is accelerating to the right so there must be friction
  5. Apr 24, 2016 #4


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    You seem to be well on the way with this. But try to give reasons for your statements.
    Why is the friction force increasing?
    Why is the normal force decreasing?
    Then looking at your diagram, why have you shown friction acting in the direction you have? (I agree with you, but you can explain why.)

    As for the direction of the forces, which can change?

    Although they only ask for one diagram, perhaps it would be interesting to draw another when the wheel has toppled much further?
  6. Apr 24, 2016 #5


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    I feel we can make that hint a bit stronger. @Vatsal , think about when the wheel is almost flat to the ground. What is the direction of its acceleration, assuming it is still not slipping?
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