Name: William B. F.
Status: educator
Age: 40s
Location: N/A
Country: N/A
Date: 2001-2002
Question:
How can I measure the rolling resistance of a gravity
powered soap box derby car?
Replies:
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.
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