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*From*: rgrandy@ruf.rice.edu (Richard Grandy)*Date*: Wed, 29 Oct 1997 07:17:12 -0600

At 10:08 PM 10/28/97, David Abineri wrote:

I have always pointed out in my Physics classes that a Displacement vs

Time graph must always be differentiable if it is to represent a "real"

situation since one cannot change instantaneously from one velocity to

another.

Today, the question of the differentiability of the Velocity vs Time

graph came into question. It seems to me that this may be non

differentiable, that is to say that acceleration may instantaneously

change from one value to another. HOWEVER, it is difficult for my high

school students to come to grips with this at the intuitive level. I

have shown such graphs to them BUT they seem to be applying their

knowledge of velocity to acceleration incorrectly. I have also said that

an object released from rest suddenly goes from zero acceleration to

9.8m/s/s but I am not sure I have convinced them yet.

Are you sure that the object goes SUDDENLY AND DISCONTINUOUSLY from zero

acceleration to 9.8 m/s/s? Is this a consequence of the Newtonian theory?

Or is it an observation? Or is this an assumption that is derived from the

math representations of the problem?

Richard Grandy

Rice University

Does anyone know of some nice way(s) of getting this point across?

Thanks for any help on this one.

David Abineri

--

David Abineri dabineri@dot-net.net

--

Janice D.Bordeaux, Ph.D.

Center for Technology in Teaching and Learning

230A Mudd Building MS-120

Rice University

6100 Main Street

Houston TX 77005-1892

Phone:713.737.5653

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