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Re: Rolling, Static, and Kinetic Friction



Well, Emilio, if there is no such thing as "rolling friction", tell us why
tires get hot -- all that thermal energy must come from work somewhere.

Jim




I like to add something about "rolling friction", as for example
when you roll a wheel (without the car, just the wheel with tire).
You may draw an exaggerated picture of an underinflated tire making
contact with the floor over a significant extent of its outside.
The picture might suggest that in order to start the rolling motion,
you must push the wheel so that the sum of push + weight falls
outside the surface of support (= contact tire/floor). THIS IS WRONG.
On this surface of contact, the tire is flat and just transmits the
internal air pressure, which is NORMAL to the floor and cannot
generate any friction force! This is the reason why an underinflated
baloon will roll down an inclined plane even for a slight angle.
Regards Emilio