What does frictionless pulley really mean?

In summary, the conversation discusses the concept of a frictionless pulley and its impact on the movement of a string. It is determined that the frictionless groove on the pulley axle provides the same result as a frictionless axle, as long as the kinetic energy of the wheel is neglected. The ideal frictionless pulley has a consistent force throughout the rope and its design does not affect its performance.
  • #1
andyrk
658
5
When we say "pulley is frictionless", do we mean its groove where the string moves or its axle or both?
 
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  • #2
The axle - but if you can neglect kinetic energy of the wheel, a frictionless groove gives the same result.
 
  • #3
mfb said:
The axle - but if you can neglect kinetic energy of the wheel, a frictionless groove gives the same result.

How? How does it give the same result as an axle which has friction, if we neglect KE of the wheel?
 
  • #4
The pulley will not dissipate any energy, and the magnitude of force is the same everywhere in the rope.
That is true for every ideal, frictionless pulley, it does not even depend on the details how you design the pulley.
 
  • #5
andyrk said:
How? How does it give the same result as an axle which has friction, if we neglect KE of the wheel?
That's not what mfb wrote. mfb said that (frictionless axle with massless wheel) gives the same result (i.e. no role in the equations) as frictionless groove.
 

1. What is a pulley?

A pulley is a simple machine that consists of a wheel with a groove around its circumference and a rope or belt that runs through the groove. It is used to change the direction of the force needed to lift an object.

2. What are the different types of pulleys?

There are three main types of pulleys: fixed, movable, and compound. Fixed pulleys have a stationary axle and are used to change the direction of the force. Movable pulleys have a freely moving axle and are used to multiply the force applied. Compound pulleys combine fixed and movable pulleys to both change the direction and multiply the force.

3. What are the conditions for pulleys to work effectively?

The two main conditions for pulleys to work effectively are having a stable support for the pulley and having a taut rope or belt running through the pulley. The pulley should also be properly sized and aligned to prevent friction and maximize efficiency.

4. How do you calculate the mechanical advantage of a pulley?

The mechanical advantage of a pulley is calculated by dividing the output force (the weight being lifted) by the input force (the force applied to the rope or belt). This ratio can also be expressed as the number of rope segments supporting the weight.

5. What are some common uses for pulleys?

Pulleys are commonly used in lifting and hoisting systems, such as in elevators and cranes. They are also used in transportation systems, such as in bicycles and cars. Pulleys can also be found in exercise equipment, window blinds, and many other everyday objects.

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