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With no need to get into the details (although the article is linked below if you wish to read it), the coefficient of rolling friction is a measurement of how much the bottom of a wheel deforms when in contact with the ground.

Learning about rolling friction, I've come across what's called the Static Coefficient of Rolling Friction. This coefficient, a measure of the amount of deformation when a wheel is standing still, is supposedly different from the regular Coefficient of rolling friction, the coefficient when a wheel is already rolling.

Why would a wheel deform more or less when rolling across the ground than when not rolling and just standing still? Why are there two different coefficients?

Thanks!

(Any theory is appreciated, doesn't necessarilly have to be the correct anser)


Article:

https://billiards.colostate.edu/physics/Domenech_AJP_87%20article.pdf

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  • $\begingroup$ @DanYand yes it's in the second page, above (3) $\endgroup$ – Joshua Ronis Dec 31 '18 at 22:22
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When rolling, energy is lost to heat by flexing the material of wheel and the surface it is rolling on. This is what heats up tires at speed. This is a kind of "friction" term, although it doesn't involve sliding of surfaces. For most wheels used in practice centrifugal force reduces the deformation of the wheel at the contact patch. At high speeds motorcycle tires have been know to go flat because the centrifugal force is enough to open the Schrader valve used to pressurize the tire. This isn't noticed until the rider slows down because at high speed the centrifugal force also keeps the tire round, as if it were still inflated. It is important to keep valve caps on the valves of fast motorcycles and cars.

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  • $\begingroup$ Hi Brent, thanks for your answer, I just liked it, but it doesn't really answer my question. I'm not referring to motorcycle tires or energy lost as heat through deformation, my question is just referring to everyday objects that roll, including tennis balls or slowly moving bycicle wheels. It can't be the centrifugal force (although that IS a good point you're making), because the constant only has two values; moving and not moving, while the centrifugal force varies with angular velocity. $\endgroup$ – Joshua Ronis Jan 1 at 14:45

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