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Why is friction going this way?

  1. Oct 25, 2011 #1
    http://imageshack.us/photo/my-images/600/unledtiw.png/

    There's no friction at wheel B because it is free to roll. But why is friction going toward the right at wheel A? It makes sense, considering that forces should balance and thus it should balance the P force, but I would imagine it's to the left, tending to oppose the motion of the fork lift going to the right.
     
  2. jcsd
  3. Oct 25, 2011 #2

    Doc Al

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    Staff: Mentor

    Friction acts to oppose slipping between surfaces. Since wheel A is turning clockwise, the tire surface would tend to slip towards the rear, thus the friction acts forward to prevent such slipping.
     
  4. Oct 26, 2011 #3
    Why doesn't wheel B have friction then?
     
  5. Oct 26, 2011 #4

    PeterO

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    Homework Helper

    I hate it when following links to images people post, my computer is about to go to an on-line poker game.
    imageshack.us is notorious for this. Certainly no way to load up a picture anyone wants me to look at.
     
  6. Oct 26, 2011 #5

    PeterO

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    Suppose there was no friction. The wheel would then spin, if it was a driven wheel, or slip along if it was a supporting wheel.
    The friction force will be in what ever direction is needs to prevent the wheel spinning - if it is a driven wheel - or slipping - if it is a support wheel.
     
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