Friction and rolling resistance, and work done queries

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  • #51
tiny-tim
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But how is that possible? Isn't the push force equal to the static friction?
which static friction?

the push force from his arm on the wheel equals the static friction force on the top of the wheel (it's just another name for it)

but that doesn't equal either of the other two friction forces (on the seat, and on the ground) unless the acceleration is zero
 
  • #52
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which static friction?

the push force from his arm on the wheel equals the static friction force on the top of the wheel (it's just another name for it)

but that doesn't equal either of the other two friction forces (on the seat, and on the ground) unless the acceleration is zero
Hi tiny tim! I thought the static friction of the push is the friction from the ground?
 
  • #53
tiny-tim
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Hi tiny tim! I thought the static friction of the push is the friction from the ground?
well, you push the wheel of a wheelchair using static friction also (and there's static friction on the seat)

anyway, nothing equals anything else unless the acceleration is zero​
 
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well, you push the wheel of a wheelchair using static friction also (and there's static friction on the seat)

anyway, nothing equals anything else unless the acceleration is zero​
Oh but since the friction acting on the wheels by the ground is also static friction, then shouldn't there be a push force that is equal to the friction on the ground? What would that push force be and since the push force is equal to the static friction on the wheel how can there be a net force?
 
  • #55
tiny-tim
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hi sgstudent! happy new year! :smile:
Oh but since the friction acting on the wheels by the ground is also static friction, then shouldn't there be a push force that is equal to the friction on the ground? What would that push force be and since the push force is equal to the static friction on the wheel how can there be a net force?
no, the push force P on the top of the wheel is forward

and the friction F from the ground is also forward

for example, if there is a horizontal wind resistance force of W, and if the acceleration is zero,

then P = F (because the angular acceleration is zero), and so P = W/2 :wink:
 

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