Solving Problems with Rolling & Slipping: Help for Friction Confusion

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    Rolling Slipping
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Discussion Overview

The discussion revolves around the concepts of rolling and slipping in classical rotational mechanics, particularly focusing on the role of friction in these processes. Participants explore the conditions under which friction is necessary for rolling motion and how it interacts with acceleration and constant velocity scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the role of friction in rolling and slipping, questioning how a body can roll without friction.
  • Another participant clarifies that once a body is rolling at a constant speed, no frictional force is necessary for its motion.
  • A third participant supports this by providing an example of a train with solid steel wheels, noting that friction is not required when the train moves at constant velocity, although real-world factors like wind resistance complicate this scenario.
  • One participant inquires about a sphere that is both rolling and sliding down an inclined plane, seeking clarity on whether friction is acting in this case.
  • A later reply suggests that if the sphere is rolling without slipping down the incline, a friction force must be present to generate angular acceleration.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of friction in various scenarios, particularly regarding rolling without slipping and the conditions of motion on an incline. The discussion remains unresolved with multiple competing perspectives on the role of friction.

Contextual Notes

Some assumptions about the conditions of motion (e.g., constant velocity, rolling without slipping) and the definitions of frictional forces are not fully explored, leaving room for further clarification.

dev70
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hi pf, the more i think i have understood classical rotational mechanics the more it turns out to be clumsy? i am just not able to understand the slipping and rolling of bodies? somewhere friction comes into play and somewhere dont?
"if a body rolls without slipping such that velocity of COM doesn't change then no frictional force acts on the body" how? why would a body roll if there is no friction?

please help me out. i am tired of reading so many books. still not able to solve numerical related to it
 
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dev70 said:
why would a body roll if there is no friction?
It's not about how it started rolling. Once it is rolling at constant speed no friction is necessary.
 
What AT said.

It actually says that in the quote...

"if a body rolls without slipping such that velocity of COM doesnt change then no frictional force acts on the body"

Consider a train that has solid steel wheels (so negligible rolling resistance)... When it accelerates it applies a force on the track in one direction, when it brakes it applies a force in the opposite direction. When it does neither and travels at a constant velocity no frictional forces are acting.

Aside: In a real train this isn't true because of things like wind resistance and rolling resistance isn't totally zero. So some force (and power from the engine) is required to maintain a constant velocity.
 
ok..if i consider a sphere rolling as well as sliding down an inclined plane? what should i interpret? friction is acting or not?
 
dev70 said:
ok..if i consider a sphere rolling as well as sliding down an inclined plane? what should i interpret? friction is acting or not?
If the sphere is rolling without slipping down the incline then there must be a friction force to produce the angular acceleration.
 

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