Rolling Fricition, Kinetic Friction

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Discussion Overview

The discussion revolves around the factors influencing rolling friction, particularly whether it depends on the surface area or size of the object. Participants explore scenarios involving different shapes and sizes, including spheres and cubes, and consider the implications of kinetic friction in these contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if rolling friction is affected by the surface area or size of the object, comparing a block and a sphere of the same mass on an incline.
  • Another participant seeks clarification on whether the block is envisioned as smoothly rolling down the incline.
  • A participant acknowledges the complexity of the motion, suggesting it may involve both sliding and rolling.
  • After reframing the question, a participant asks if rolling friction varies between two spheres of different radii but the same mass, under specific conditions regarding interatomic forces.
  • One participant introduces a scenario involving railway freight car wheels of different diameters, questioning how this would affect rolling resistance.
  • A later reply confirms the focus on perfect disc wheels in the previous question.

Areas of Agreement / Disagreement

The discussion contains multiple competing views regarding the influence of object size and shape on rolling friction, and no consensus has been reached on the specific conditions or outcomes.

Contextual Notes

Participants express uncertainty about the assumptions regarding the nature of rolling friction and the conditions under which it is analyzed, particularly in relation to the effects of surface area and material properties.

Prannoy Mehta
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Does rolling friction depend on the surface area? In other words, the size of the object placed? If I had a block and sphere of the same mass. Without static and kinetic friction coming into play. Which would experience greater rolling friction if they were on the same incline and of the same material and mass?

If I had a similar scene with a cube and cuboid (The base area of the cuboid is more, they are made of same materials and have the same mass.). Which would go down first if kinetic friction is considered? Assuming no toppling.
 
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Are you picturing your block smoothly rolling down the incline?
 
Yes. Toppling over and over again. (With a good speed) Giving a picture that it is rolling.
 
That sounds like a combination of sliding and rolling, at least.
 
Yes, very true. I forgot about it. So I will reframe my first question.

Does rolling friction depend on the surface area? In other words, the size of the object placed? If I had two spheres (With radii r1 and r2. r1>r2) of the same mass. Without static and kinetic friction coming into play. Which would experience greater rolling friction if they were on the same incline and have similar forces between the atoms of one another? (I mentioned the latter condition to simply ensure that there is nothing to do with the interatomic forces between the atoms of the spheres with that of the plane. As the materials will be different. If not appropriate please modify the condition to convey the same message.)
 
If the wheels on a railway freight car were swapped with wheels similar but of a greater diameter, how will its rolling resistance be expected to change? ... does that say what you seek?

I could only guess the answer, hopefully someone else can help you with this.
 
Yes, precisely. Just assuming the wheels are perfect discs.
 

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