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Re: Kinematics First



I just don't see how you can introduce Newton's Laws successfully if
students don't understand ACCELERATION. I spend considerable time working
on just the concepts of speed, velocity, acceleration. If students can
consistently recognize situations in which an object is accelerating I'm
happy. If they can then tell me the direction of the acceleration, they
'have it'. At that point I can introduce kinematics and then dynamics. I
want them to recognize situations where a non-zero Net Force must exist or
to recognize situations where the forces must vector sum to zero. I want
them to recognize when a set of forces will cause a change in the motion.
Since these dynamics goals require an understanding of acceleration, I still
think acceleration is the right starting point.

Unless you have tested (conceptual style questions) for student
understanding of acceleration, you would probably be surprised at how
difficult a concept it is. I use my favorite motion--ball thrown straight
up and later caught--to test this. It is amazing how difficult it is for
students to understand that (out of the hand) the ball is always
accelerating downwards. We go over and over 1-dimensional accelerations (if
an object speeds up the acceleration is in the direction of motion and if it
slows down the acceleration is in the opposite direction of the motion) but
the concept that the ball going up is accelerating downward is _really_
difficult. Ultimately, one shouldn't jump into the kinematics equations
without knowing that most of the class can deal with acceleration on this
conceptual level.


Rick

*********************************************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, Indiana
rtarara@saintmarys.edu
********************************************************
Free Physics Educational Software (Win & Mac)
www.saintmarys.edu/~rtarara/software.html
NEW: Mac versions of Lab Simulations
********************************************************

----- Original Message -----
From: "Steve Clark" <sclarkphd@MINDSPRING.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Monday, September 16, 2002 10:24 PM
Subject: Kinematics First


I'd like some input on why we traditionally teach kinematics first. I'm
just finishing up my kinematics section for this new school year.
Normally I don't do kinematics first. I usually begin with vectors and
then move into Newton's 1st & 3rd laws (generally with objects that are
in statics equilibrium) and then go o kinematics. The few times I've
tried to do the motion study first, I've frustrated me and my students.
They don't come to me as good problem solvers. Furthermore, even though
the ideas of speed and acceleration are "common" in that everybody
"knows" the words, the concepts are not easy for first year high school
physics students (11th & 12th graders). Also, I'm not sure how to
explain free fall (and projectiles) without 2nd law. So, I've generally
waited until a couple of months into the year before I begin to tackle
those topics.

But this year, after we bought brand new texts, I thought I'd follow
the traditional path once again. And now I'm grading a set of exams
that are les than good. So, my question is, why do the textbooks almost
all follow the same strategy. And does it work for you better than it
does for me? Just wondering. I know what I'm going to do next year.


Steve Clark, Ph.D.

The box said "Requires Windows 98 or better,"
so I bought a Macintosh.