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One think I do is make a clear distinction between "speed" and
"velocity", so I wouldn't talk about negative speed, only negative
velocity. Here speed is what the car speed-o-meter reads.
cheers,
joe
On Wed, 19 Nov
2003, Bob LaMontagne wrote:
I find this to be the case with my non-science majors. They never fully
understand the concept of 'acceleration'. But they can easily grasp the
idea that when an object falls, it picks up 10 m/s in speed every
second. They can work out fairly sophisticated problems just by making
out a little table with the speed being 0 initially, 10 m/s after 1 sec,
20 m/s after 2 sec, etc. It also doesn't bother them in the least to
think of the speed decreasing by 10 m/s every second as a ball rises.
The transition from positive to negative speeds at the top never bothers
them - in fact they usually suggest it before I do. But - mention
acceleration and they're totally confused - especially the idea that the
acceleration is g at the peak of the balls motion. They need to deal
with finite intervals. I think this is one of the advantages of the
momentum approach to N2.
Bob at PC
Joseph Bellina wrote:
I agree with your suggestion. I also think we should not use Newton's
original work, just as most have found they can't use Feynman's text.
I wonder what would happen if we eliminated the work acceleration and
only used change in velocity, or if you wanted change in momentum. By
eliminating the work you would eliminate the task of developing a
conceptual understanding for it. I would also like to eliminate the
word displacement, since it is just the change in position. It seems to
me that students can handle vector position and vector velocity pretty
well. They can do change in position and change in velocity too, but
vector acceleration, the change of a change is just too much
for many of them to conceptualize. I'd rather just talk about the rate of
change of velocity, or of momentum. The term displacement is, in my mind,
superfluous.
cheers,
joe
On
Wed, 19 Nov 2003, Chuck Britton wrote:
If I understand John correctly -
He is trying to DOWNplay the equation that most of us rattle off as N2, F=ma.
A MUCH better representation of Force is Newton's own version
F = delta p/delta t
Even for those intro students who are being introduced to SR (or GR),
it is VERY good pedagogy to use the momentum formalism in favor of
the acceleration approach.
Most of us realize how much trouble acceleration causes for our students.
Example - a ball at the top of it's trajectory. What is the
force/acceleration of the ball AT THAT INSTANT!!!
If you think that most of your student 'get this' you are sadly mistaken.
Drawing a momentum vs time graph (or more commonly,velocity vs time)
Gives them a visual picture that answer the difficulty for some/many students.
Acceleration is a VERY difficulty concept.
Momentum is a MUCH simpler and basic concept.
USE it ! ! ! !
OK, ya'll, at 9:56 AM -0500 11/19/03, Bob Sciamanda wrote:
I respect your free choice to use this conceptual model of F=ma in
component form. As with all conceptual models, this is a matter of
taste and free choice; the testable physics lies in the quantitative
relations connecting measurables.
--
Chuck Britton Education is what is left when
britton@ncssm.edu you have forgotten everything
North Carolina School of Science & Math you learned in school.
(919) 416-2762 Albert Einstein, 1936
Joseph J. Bellina, Jr. 574-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556
Joseph J. Bellina, Jr. 574-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556