# Why is friction going this way?

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.

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Doc Al
Mentor
but I would imagine it's to the left, tending to oppose the motion of the fork lift going to the right.
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.

Why doesn't wheel B have friction then?

PeterO
Homework Helper
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.
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.

PeterO
Homework Helper
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.
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.