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Re: steering



Grabbing the bull (on wheels) by the horns:

1) Consider a wheel hanging in free space (its CM at rest) and spinning with
its (horizontal) angular velocity vector pointing in the NW direction. If
you bring a horizontal floor up from below, the spinning wheel exerts a
frictional force on the floor in the SW direction, so that the floor exerts
a NE force on the wheel, and the wheel's CM moves forward (rolling/slipping)
toward the NE.

2) Now consider the same wheel spinning in free space as before, but now -
in addition to its spinning - its CM is translating in the N direction
(perhaps because it is part of a freely moving car). Now when you bring up
the floor, all of the above still happens (the wheel is pushed in the NE
direction because of the SW frictional force of the spinning wheel on the
floor) - but in addition the Northerly motion of the wheel body gives rise
to a frictional force from the floor on the wheel in the Southerly
direction. The vector sum of the NE'ly and S'ly forces of the floor on the
wheel yields a net force on the wheel which has a strong component in the SE
direction (the "centripetal" direction).

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.velocity.net/~trebor/
trebor@velocity.net