Coefficient of Rolling Friction

[Everydaylearning]

Is the coefficient of rolling friction the same when the object to be pushed is as rest as it is when the object is already in motion. Intuition tells me the rolling resistance is higher at rest, but I cannot find a resource to prove this. Any help is appreciated.

https://www.engineeringtoolbox.com/rolling-friction-resistance-d_1303.html

 

[JStephen]

My guess is that it would be a lot more variable when stopped, due to minor imperfections- assuming hard surfaces like the steel wheel on steel rail.
Note that your reference shows car tires varying in rolling resistance depending on speed. Part of the issue there is damping effects in the tires.
In the case of bicycle tires, I have read speculation that you get similar effects due to vibration.

 

[hoshang]

Is the coefficient of rolling friction the same when the object to be pushed is as rest as it is when the object is already in motion.

Static & kinetic friction comes from rigid wheel and plane.
Rolling friction comes from slight deformations of the wheel and plane.
Rolling friction is typically much lower than static or kinetic friction.

 

[epoxybot]

I rather like the 2nd explanation in this thread Link

At a bare minimum, I would think the energy required to overcome the van der Waals force/s would be associated with Static Friction.

 

[GregLocock]

Moving /friction/ is always less than, or at most equal to, static, because in the limiting case as v tends to zero dynamic becomes static. That's sort of playing with words. bearing in mind tho that the rolling resistance of many practical systems also includes a damping term.

Cheers

Greg Locock


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[Everydaylearning]

I think my post may have been misunderstood. I am wondering about the value of rolling friction from rest, not how it is different from sliding friction. I think that the answer is that friction is infeticemal before rolling starts

 

[LittleInch]

I think the issue here is whether you are truly talking about only rolling resistance or whether you have some other form of friction involved.

I.e. are we looking at something like a steel ball or maybe a wheel that has no axle or something else.

If the object when it is moving has only rolling friction then the value of the static friction is quite low. The item once moving on a flat surface will eventually stop due to this rolling friction but to start again would be easy. The coefficient of friction I can't see changing, just the friction value, as at rest there is no rolling friction by definition.

If you start to include axles and bearings then you start to include kinetic friction in many instances which confuses the picture and introduces higher levels of static friction than the simple rolling itself.


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[BUGGAR]

If the rolling resistance (avoiding the word, friction) is not less than resting resistance, would not the rolling thing just keep on rolling forever, or at least approach zero velocity asymptotacally(sp)?

 

[BridgeSmith]

I would consider the term "rolling friction" to be a misnomer, at least in the context as I understand it. For a wheel that is rolling, the friction value would be essentially that of static friction, since the surfaces are in static contact within the contact patch at any given point in time.

Rolling resistance of a wheel, the drag due to plastic deformation of the wheel and contact surface, is not friction, and should not be evaluated as such.

 

[charliealphabravo]

I'm with HR10. The standard physics approach is to use the static coefficient of friction for a rolling wheel which is presumed to be the same as for a wheel that is not rolling.

Whether it is appropriate to include the CRF in the friction coefficient would seem to depend on questions regarding the speed of the wheel, rate of surface deformation, relative elastic modulus of the two materials, and presence of fluids which can create suction in the rolling scenario.

When you actually attempt to measure the static coefficient of friction for two materials there is considerable variability around the published values, mostly related to surface conditions I suppose. I think this variability will overshadow the subtle effect OP is asking about.