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Regarding Rolling static, and Kinetic friction:
Here's what I got from our discussion of it in physics. Rolling friction is caused by the cohesion of the two surfaces; as the wheel rolls forwards, the back edge has to lift up off of the floor. This takes a force. This effect is also present in static and kinetic friction, but it is drowned out by the mu*N component. An important factor in cohesion is the temperature of the surfaces; the hotter the surfaces, the better they stick. This means that as you increase the velocity of the object, friction causes it to heat up, and the cohesion increases. Also friction is extremely complicated and from what I understand there are no good models for it to date in physics. All the f=mu*N and f=b*v^2 stuff are just empirical approximations.
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