Re: L2-"Negotiating" a curve.

[Rick Tarara <rbtarara@SPRYNET.COM>]

----- Original Message -----
From: Arlyn DeBruyckere <arlynd@HUTCH.K12.MN.US>
To: <PHYS-L@lists.nau.edu>

> I don't see where Hewitt blew it.  We have an object (as I understand
> the question) traveling at a uniform speed in a circular motion.  The
> net force necessary to provide this motion is toward the center of the
> circle (center directed - centripetal).  The acceleration of the object
> is toward the center if we use the classical frame of reference to be
> the earth standing still.  If there were no net force the object would
> continue in a straight line but in this case since the object is curving
> toward the center of the circle the force is toward the center of the
> circle - centripetal force.
>
> --
> Arlyn DeBruyckere

Arlyn,

I suspect you are new to the list (this topic is discussed often ;-).  The
problem with labeling a force vector as the centripetal force is that it
instill in students the idea that there is a force in nature called the
centripetal force.  We know that for uniform circular motion there has to be
a net force directed towards the center of that motion in order to produce
the needed centripetal acceleration, but that net force must be identifiable
as a gravitation, friction, a tensional, a push, a pull, etc. or a
combination of such.  Look at the motion of a person riding a Ferris Wheel
and try to identify the forces that cause the centripetal acceleration as
the wheel rotates.  Those forces keep changing--being sometimes the 'weight'
of the person, sometimes the bottom of the chair, sometimes the back of the
chair, sometimes maybe just friction, and usually a combination of at least
two of the above.  Just drawing an force vector towards the center and
labeling it Centripetal Force is insufficient to fully understand and
appreciate such a situation.

Rick

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Richard W. Tarara
Department of Chemistry & Physics
Saint Mary's College
Notre Dame, IN 46556
219-284-4664
rtarara@saintmarys.edu

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