What does frictionless pulley really mean?

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The discussion revolves around the concept of a frictionless pulley in physics, specifically questioning the implications of frictionlessness in both the groove and the axle of the pulley system.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the definitions and implications of a frictionless pulley, questioning whether it refers to the groove, the axle, or both. There are inquiries about how neglecting kinetic energy affects the system's behavior and whether a frictionless groove can yield the same results as a frictionless axle.

Discussion Status

The discussion is active, with participants seeking clarification on the relationship between friction in the axle and groove. Some have provided insights into energy dissipation and force magnitude in ideal pulleys, while others are probing deeper into the reasoning behind these assertions.

Contextual Notes

Participants are navigating assumptions about energy conservation and the ideal conditions of pulleys in physics problems, with a focus on the implications of neglecting certain factors.

andyrk
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When we say "pulley is frictionless", do we mean its groove where the string moves or its axle or both?
 
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The axle - but if you can neglect kinetic energy of the wheel, a frictionless groove gives the same result.
 
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?
 
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.
 
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.
 

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