Reply to ""Physics" Question"

Jack LOGR Forum Member DIGITAL SUBSCRIBER

Originally Posted by John Ochab:

There are two types of frictional valves called the coefficient of friction one is a static value and one is a dynamic value.

I would be interested in where you got your information from. Static and Kinetic (dynamic) friction is for flat surfaces in contact. So, it could take say 40 lbs of force to start a box sliding across the floor (static friction) but once it is moving it may drop to 30 lbs of force to keep in moving (kinetic friction).

That does not apply to a wheel rolling on a flat surface. Ignoring wind, rusty rails, friction within the axle bearings, etc. you are left with rolling friction. The coefficient of rolling friction for steel wheels on steel rails averages 0.001. So for a 100 ton car it would take 200 lbs of force to get it moving (100 x 2000 x 0.001).

Jack

7/16/1410:25 PM

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