Quote Originally Posted by Carnel View Post
Hi Tony,

Thank you for your extensive explanation. For me there is a missing link of thinking between the following texts:
.......................................

I refer to figure 3. If the belt in fig 3 runs upward there is a slipping force downward at point 2 and a slipping force upward at point 1 resulting in a clockwise torque. This torque combined with the upward moving of the belt drives the belt to the left.

Harry Croon
Harry,

I do not know how else to explain it. I would suggest that you think about it in terms of velocities rather than slip forces. You have not said what you mean by slipping force when you talk about upward or downward forces. You have to specify whether you mean the force on the belt or the force on the pulley, these are equal and opposite.

Here is another way to think of it. When you have slip the the tendency of the system will be to eliminate that slip, in this case that means matching the velocities of belt and pulley which is achieved by point 2 trying to move to the top of the crown.

PS. My first paragraph assumes that your reference to up and down refers to my drawing and not laterally on the pulley.