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-----Original Message-----
From: Rick Tarara [mailto:rtarara@SAINTMARYS.EDU]
Sent: Tuesday, September 17, 2002 8:54 AM
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.