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boredaxel
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If a string around a pulley is pulled without slipping, I am wondering if there is any frictional force acting on the string by the pulley. If there is, will it appear in calculations? Thanks in advance
Sure, otherwise the string couldn't turn the pulley.boredaxel said:If a string around a pulley is pulled without slipping, I am wondering if there is any frictional force acting on the string by the pulley.
Not usually. (It's static friction and does no work.)If there is, will it appear in calculations?
No, it just transmits the string tension to the pulley.boredaxel said:but wouldn't the static friction appear in torque calculation?
No.Also what if the string is assumed to be massless, doesn't that implies no friction and so the pulley shouldn't be able to turn?
Doc Al said:No, it just transmits the string tension to the pulley.
Care to explain this? I can't really visualize it. Thanks
boredaxel said:but wouldn't the static friction appear in torque calculation?
Also what if the string is assumed to be massless, doesn't that implies no friction and so the pulley shouldn't be able to turn?
Doc Al said:Typical assumptions (in intro courses) are that strings are massless (and thus have the same tension throughout) …
Absolutely, but you generally don't need to explicitly consider static friction. The forces exerted on the pulley are represented by the tensions in the string.tiny-tim said:If the pulley has mass, and if you need to calculate the energy or angular momentum of the pulley, then yes, the friction is an external force on the pulley, and will provide a torque to the pulley.
But not if the pulley is massless, a common assumption as you point out. I was waiting for the OP to bring up the issue of a massive pulley so I could qualify my statement. (One step at a time.)but a string touching anything (like a pulley) with friction will have different tension on either side, even if the string is massless.
Doc Al said:I was waiting for the OP to bring up the issue of a massive pulley so I could qualify my statement. (One step at a time.)
A frictional pulley system is a mechanical system that uses pulleys and ropes or belts to transmit force and motion. In this system, the pulleys have friction between the ropes and the pulley surface, which affects the tension and movement of the ropes.
The friction in a pulley system can be calculated using the formula F = μN, where F is the frictional force, μ is the coefficient of friction, and N is the normal force. The normal force is the force perpendicular to the surface of the pulley, and the coefficient of friction depends on the materials in contact.
Friction is important in pulley systems because it affects the efficiency and effectiveness of the system. Too much friction can lead to energy loss and decreased performance, while too little friction can cause the ropes to slip and the system to fail.
Friction in a pulley system can be reduced by using lubricants on the pulley surface, choosing materials with low coefficients of friction, and ensuring proper alignment and tension of the ropes. Regular maintenance and cleaning of the pulley system can also help reduce friction.
The angle of the ropes in a pulley system can affect friction by changing the normal force and the direction of the frictional force. As the angle increases, the normal force decreases, and the frictional force acts more parallel to the surface, increasing the friction. This can lead to higher tension and potential slipping in the ropes.