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From: (Jobst Brandt)
Subject: Re: Rolling Resistance question?
Date: 16 Feb 2001 21:22:51 GMT

David L. Johnson writes:

>> And, BTW, I have two physics books here both of which define
>> rolling friction as the interaction between the road and the mass
>> while moving.

> That's a little vague, though, isn't it?  "interaction" could mean
> many things, and does, depending on materials.  Your basic physics
> text doesn't consider pneumatic tires and the resulting hysteresis
> effects.  They usually deal with railroad cars with steel wheels.

Even there the losses are in the steel rail and wheel but even more so
the depression of the ground under the rail.  Most people have at one
time or another seen a train pass, either at a crossing or station,
and noticed the vertical deflection of the rail.  This motion is
highly damped and absorbs energy.  Each wheel is constantly climbing a
grade as it progresses in its depression.  Therefore, I find the
physics book reference a clear indication to not use these books.

The deflection of a rail is a classic elastically supported beam,
directly analogous to the rim of a bicycle wheel, except that a
bicycle wheel is round.  The deflections are the same, however.  There
is a low spot in the middle of the load and a slight hump to either
side, the rest of the rail is unaffected, other than length change by
cosine error, a trivially small amount.

Jobst Brandt      <>

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