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Name: William B. F.
Status: educator
Age: 40s
Location: N/A
Country: N/A
Date: 2001-2002

How can I measure the rolling resistance of a gravity powered soap box derby car?

There are several convenient ways I can think of. The simplest might be to pull it using a scale at a constant speed on a level surface. You could try this at different speeds to see if the friction changes.

Another method would be to roll the car down an inclined plane whose angle is adjusted so the car goes at constant speed. When that happens, the tangent of the angle of the plane relative to the horizontal is just the coefficient of rolling friction.

Notice that to start the car from rest the plane must be at a larger angle than needed to keep it moving at constant speed; this illustrates that static friction is larger than kinetic friction.

Best, Dick Plano...

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