Is Rolling Resistance N+Ft or Separate Forces in Tire Dynamics?

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Discussion Overview

The discussion revolves around the dynamics of rolling resistance in tires, specifically whether rolling resistance can be considered as a combination of normal force and frictional force or as separate forces. Participants explore the implications of these concepts on tire behavior during rolling without slipping, including the roles of static friction, hysteresis, and deformation.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that rolling resistance can be viewed as a combination of normal force (N) and frictional force (Ft), while others suggest they are separate forces affecting tire dynamics.
  • There is discussion about the conditions required for a tire to roll without slipping, including the need to apply a force that overcomes the rolling resistance while remaining below the threshold defined by static friction.
  • Participants question whether the normal force is constant across different points on the tire and express confusion about the maximum normal force's location in relation to points A, B, and C in the provided diagram.
  • Some participants mention that rolling resistance includes components due to hysteresis and sliding friction, complicating the calculation of the forces involved.
  • There are corrections regarding the locations of maximum and zero normal forces, with some participants expressing uncertainty about their understanding of the diagram and the forces at play.
  • One participant seeks recommendations for literature on tire kinematics to better understand the concepts discussed.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether rolling resistance should be treated as a combination of forces or as separate entities. There is also disagreement regarding the locations of maximum and zero normal forces, indicating a lack of clarity on these points.

Contextual Notes

Participants express confusion over the relationships between the forces involved in rolling resistance, including the effects of hysteresis and the conditions for rolling without slipping. The discussion highlights the complexity of tire dynamics and the need for precise definitions and understanding of the forces at play.

Who May Find This Useful

This discussion may be useful for individuals interested in tire dynamics, mechanical engineering, and the physics of rolling motion, particularly those seeking to understand the interplay of forces in tire behavior.

LLT71
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http://imageshack.com/a/img923/733/FJKAqj.jpg
so here is the deal. is rolling resistance N+Ft or are they "separate" in a means of: N part is for static friction = mu*N and Ft is part of rolling resitance=coefficient of rolling resistance*Ft so that in order for tire to start rolling without slipping do I need to apply such force that overcomes Ft*coeff of rolling resistance. but at the same time that applied force has to be less than mu*N?
2. is N equal for every point from point C to B (see picture) and why?
3. why its the point of most interest just point B (like in this picture, and similar ones explaining rolling friction)?
 
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LLT71 said:
http://imageshack.com/a/img923/733/FJKAqj.jpg
so here is the deal. is rolling resistance N+Ft or are they "separate" in a means of: N part is for static friction = mu*N and Ft is part of rolling resitance=coefficient of rolling resistance*Ft so that in order for tire to start rolling without slipping do I need to apply such force that overcomes Ft*coeff of rolling resistance. but at the same time that applied force has to be less than mu*N?
2. is N equal for every point from point C to B (see picture) and why?
3. why its the point of most interest just point B (like in this picture, and similar ones explaining rolling friction)?
See if section 4.1 of https://www.physicsforums.com/insights/frequently-made-errors-mechanics-friction/ helps.
 
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I"m not sure how you calculate rolling resistance from that diagram. Part of rolling resistance is due to hysteresis, and part due to sliding friction. The force during radial deformation is greater than the force during recovery, lost to heat (hysteresis). There's also loss due to deformation along and across the tread, some of this loss is due to hysteresis, some due to sliding friction as the tread deforms and recovers.

The normal force at A and C is zero. The maximum normal force occurs near B.

Correction - the normal force at B and C is zero. The maximum normal force occurs near A.
 
Last edited:
rcgldr said:
I"m not sure how you calculate rolling resistance from that diagram. Part of rolling resistance is due to hysteresis, and part due to sliding friction. The force during radial deformation is greater than the force during recovery, lost to heat (hysteresis). There's also loss due to deformation along and across the tread, some of this loss is due to hysteresis, some due to sliding friction as the tread deforms and recovers.

The normal force at A and C is zero. The maximum normal force occurs near B.
say I am stupid but why forces at point A and C are zero? and how do I know whitch force I must apply to tire in order to roll it without slipping? what I must overcome with that force? so confusing... also, can you recommend me some books that explain tire kinematics? thank you!

@haruspex thank you!
 
rcgldr said:
The normal force at A and C is zero. The maximum normal force occurs near B.
I think you have A and B swapped over relative to the diagram.
The maximum normal force should be right in the middle, no? But it will be greater a small distance x in front of that than at the same distance behind it.
 
rcgldr said:
The normal force at A and C is zero. The maximum normal force occurs near B.
Correction - the normal force at B and C is zero. The maximum normal force occurs near A.
LLT71 said:
forces at point A and C are zero?
haruspex said:
I think you have A and B swapped over relative to the diagram.
I forgot the ordering of points in the diagram, I had thought it was A, B, C, right to left, not B, A, C right to left, so I got A and B swapped. I struck through the incorrect statement and added what should be a correct statement.

LLT71 said:
how do I know whitch force I must apply to tire in order to roll it without slipping?
It's complicated. You have hysteresis effects related to deformations along the sidewalls and across and in the direction of tread. There's also some sliding friction along the tread surface as it deforms, but according to wikipedia, most of the losses to heat are due to hysteresis.

http://en.wikipedia.org/wiki/Rolling_resistance
 
rcgldr said:
It's complicated. You have hysteresis effects related to deformations along the sidewalls and across and in the direction of tread. There's also some sliding friction along the tread surface as it deforms, but according to wikipedia, most of the losses to heat are due to hysteresis.

http://en.wikipedia.org/wiki/Rolling_resistance

ok,and what about my picture in first post; is it decently okay if I say that I must apply moment (Mo=Fo*rd) that will overcome N*f in order to have just pure rolling but at the same time I have to be careful that force Fo=Mo/rd has to be ≤μstatic*N (cause it will cause additional slipping, something like burnout)?
 

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