# If the friction coefficients depend on the object's property, why do they change in sliding & rolling, despite the object being same? [duplicate]

I know that when you roll an object instead of sliding it reduces the friction you can easily move an object. Consider the object to have a weight $W$ on a horizontal surface and the two objects have coefficient of friction of $\mu$. Thus the friction force $f$ should be: $$f=\mu W$$ In order for the friction to change, either $\mu$ or $W$ has to change and since $W$ does not change when rolling $\mu$ changes. My question is ,$\mu$ depends on the property of the materials not their orientation or their surface area of contact. So what has changed in order for $\mu$ to change? Does $\mu$ depend on other factors. The same question for static friction $\mu_{s}$and kinetic friction $\mu_{k}.$