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Dear all,
I have a very simple question. The rolling resistance (rr) of, say, a car, is defined as being proportional to the normal force/weight of an object. That seems reasonable:
##F_{rr} = C_{rr} \times F_N##
The coefficient [itex]C_{rr}[/itex] is a constant, depending on the materials. But now a simple yet confused question: what's [itex]F_{rr}[/itex] for a car standing still on a road? According to the formula, the car is subject to a [itex]F_{rr}[/itex] due to the normal force/weight. On the one hand, this seems not so silly, because the tires are deformed, but on the other hand: which force is then opposing this [itex]F_{rr}[/itex] such that the car doesn't move? And how does this rolling resistance develop when the car starts to move? I guess the direction here is important; the definition above is not a vector equation (), so maybe I'm confused about the directions. Also, forces like the normal force are "reactive forces", which adjust themselves to the situation, but in this case the movement is perpendicular to the normal force.
I'm asking this as a physics teacher :)
I have a very simple question. The rolling resistance (rr) of, say, a car, is defined as being proportional to the normal force/weight of an object. That seems reasonable:
##F_{rr} = C_{rr} \times F_N##
The coefficient [itex]C_{rr}[/itex] is a constant, depending on the materials. But now a simple yet confused question: what's [itex]F_{rr}[/itex] for a car standing still on a road? According to the formula, the car is subject to a [itex]F_{rr}[/itex] due to the normal force/weight. On the one hand, this seems not so silly, because the tires are deformed, but on the other hand: which force is then opposing this [itex]F_{rr}[/itex] such that the car doesn't move? And how does this rolling resistance develop when the car starts to move? I guess the direction here is important; the definition above is not a vector equation (), so maybe I'm confused about the directions. Also, forces like the normal force are "reactive forces", which adjust themselves to the situation, but in this case the movement is perpendicular to the normal force.
I'm asking this as a physics teacher :)