Coefficient of 'Kinetic' Rolling Friction(?)

[mart7x]

When looking at rolling objects, the force of rolling resistance is determined by a coefficient of rolling friction. Is this coefficient constant for an object when both stationary and moving? Or is there a separate static and kinetic coefficient as there is with sliding friction?

I am asking this because the research I have done into this so far, I have only found talk of just the one coefficient. However an object on wheels much surely require a larger force for initial acceleration from stationary than to maintain velocity once in motion? If you could recommend any literature on this subject that would be very kind, I have searched through a number of books on Statics but can't seem to find much information.

Martin

 

[xxChrisxx]

Unless it's moving it's not rolling.

 

[mart7x]

So... for a wheel for example: Stationary - Coefficient of Static Friction, Rolling - Coefficient of Rolling Friction.

If a surface was made of wood, a wooden wheel would have the same resistive force as a block of wood when resting stationary on top (assuming they have the same mass)?

 

[rcgldr]

It should be called rolling resistance, not rolling friction, since that can cause it to be confused with actual friction (static or dynamic).

You could consider "static" rolling resistance to be related to the amount of torque or force it takes to overcome a "flat' spot at the bottom of the wheel if it's been at rest for some time. For example a cold tire on a car that's been at rest overnight. Normally rolling resistance is considered a constant fraction of the weight on the wheel (or the force between tire and pavement). It may vary a bit with speed, but I don't know the formula.

 

[PJC01]

,

The coefficient of rolling friction is a constant value that represents the relationship between the force of rolling resistance and the weight of the object. This coefficient does not change for an object whether it is stationary or in motion. However, in order to calculate the force of rolling resistance, we need to consider both the coefficient of rolling friction and the normal force acting on the object. The normal force is the force exerted by the surface on the object, and it can change depending on whether the object is stationary or in motion.

In the case of an object on wheels, the initial acceleration from stationary does require a larger force as compared to maintaining velocity once in motion. This is because the normal force acting on the object is greater when it is stationary, as the wheels are not yet supporting the weight of the object. Once the object is in motion, the normal force decreases as the weight is distributed between the wheels and the surface. This is why it may seem like the coefficient of rolling friction is changing, but in reality, it is the normal force that is changing.

As for literature on this subject, I would recommend looking into textbooks on mechanics or engineering mechanics, as well as research articles on rolling resistance and friction. I hope this helps clarify your understanding of the coefficient of rolling friction.