A patient in a wheelchair notices his wheels are sometimes warm after he travels. If the patient traverses the same distance across the same material surface, which situation would his wheels be the hottest after completion?

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Correct Answer: C. Rolling backwards on an even floor.
Friction is the cause of the heated wheels. The heat energy produce by friction is the work done by frictional forces.

Because the distance and the surfaces are the same, all we need to focus on is the normal force. Normal force is the equal but opposite force a body, generally it’s weight, applies to the contacting surface. On any incline only a fraction of the weight, Wa, is applied to the inclined surface. Assuming the acceleration of his rolls is not directly into the ramp, you will have the greatest friction on a flat surface. This is apparent when we tend to see objects sliding on ramps and not as much on the floor.

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