Re: Choosing Coordinate Systems

[Joseph Bellina <jbellina@SAINTMARYS.EDU>]

I'm not sure they would understand in the circular motion case that the
intended motion is toward the center...since motion, a vague term at
best, generally means velocity, or more vaguely "where it is going".  It
seems to me that your have simply replaced the word acceleration with
"intended motion", which may be useful since they have trouble with the
concept of acceleration.  Or it may not, since now there are two sets of
words being used for the same concept, and one set, "intended
motion" could be confused with velocity.

joe

On Mon, 24 Sep 2001, Michael
Edmiston wrote:

> This is partly to echo what has already been said, but to add slightly
> different wording.
>
> I agree it usually leads to simpler math if we choose one of the axes
> parallel to the acceleration.  But what if there isn't any acceleration or
> motion?"
>
> Therefore, I say... It usually leads to simpler math if you align one axis
> with the motion or the intended motion.  Then I give some examples when
> appropriate.  Examples:  If I am trying to pull a sled using a rope, the
> intended motion is along the ground; not in the direction I am pulling with
> the rope.  If I am trying to push a box up a ramp, the intended motion is
> parallel to the ramp.  On a banked highway, the intended motion is not
> up/down the incline, it is toward the center of curvature.
>
> Of course things do not always go where we intend them to go... but I think
> this wording reaches a few more students than saying "parallel to the
> acceleration."
>
>
> Michael D. Edmiston, Ph.D.              Phone/voice-mail:       419-358-3270
> Professor of Chemistry & Physics        FAX:                    419-358-3323
> Chairman, Science Department            E-Mail                  edmiston@bluffton.edu
> Bluffton College
> 280 West College Avenue
> Bluffton, OH 45817

Joseph J. Bellina, Jr.               219-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556