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Homework Help: Friction increase decrease Help

  1. Oct 15, 2011 #1
    1. The problem statement, all variables and given/known data

    In Fig. 6-12, if the box is stationary and the angle θ between the horizontal and force is increased somewhat, do the following quantities increase, decrease, or remain the same?


    a) Fx
    b) fs
    c) FN
    d) fs, max
    e) If, instead, the box is sliding and θ is increased, does the magnitude of the frictional force on the box increase, decrease, or remain the same?

    3. The attempt at a solution

    This is correct. But why for a, b, d. Please be help.
    a) decrease
    b) decrease
    c) increase
    d) increase
    e) increase
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 16, 2011 #2
    See the sketch below,

    Attached Files:

  4. Sep 30, 2012 #3
    I am resurrecting this old post because I am on the same problem. I understand all of these answers except for b. I do not understand and it seems counter intuitive to me to think that the higher my angle of force is on a box the lower the friction force becomes. Wouldn't that mean that i would have an easier time moving something by pushing on it from above than I would from the side?
  5. Sep 30, 2012 #4
    Yes, but you are not going much further since Fx is reduced. If you are lifting from above, you are not moving to where you are intended to go.
  6. Sep 30, 2012 #5
    So the force decreases and that's why the friction force decreases?
  7. Sep 30, 2012 #6
    Yes, friction depends on Pressing force or Normal force. Less pressing force means less friction.
  8. Sep 30, 2012 #7
    See that's why this makes no sense to me. Because we are increasing that angle which means I am pressing on it with more and more weight.... I thought this made sense but now its clear to me that I don't know why that would decrease. Because its not saying im lifting the box it says I am esentually going from pushing on the corner to standing on top of the box.
    Last edited: Sep 30, 2012
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