How do friction and normal force change when the applied angle increases?

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jonochui
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Homework Statement



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?

http://i.imgur.com/YcOFS.jpg

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?

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
 

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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?
 
vysero said:
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?

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.
 
So the force decreases and that's why the friction force decreases?
 
vysero said:
So the force decreases and that's why the friction force decreases?

Yes, friction depends on Pressing force or Normal force. Less pressing force means less friction.
 
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 I am lifting the box it says I am esentually going from pushing on the corner to standing on top of the box.
 
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