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Re: [Phys-L] Sequence



Just thinking at loud here...

What if you start by defining constant velocity and showing what its
position and velocity graphs look like. Then define constant, non-zero,
positive acceleration and show what its position and velocity graphs look
like. At this point, you have invested maybe 3 class periods if you go
slow.

Then move on to forces, momentum, energy, circular motion, gravitation,
whatever you like, returning to kinematics as later, say before you teach
projectile motion but after you teach vectors.

This way, you would have the vocabulary of kinematics in place but not the
equations. You would get to say things like: when no unbalanced forces act
on an object, its velocity graph looks like this,or like this but never
like that.

It feels to me that you could teach a lot of physics before you needed any
further kinematics treatment.


On Wed, Mar 19, 2014 at 6:29 PM, Robert Cohen
<Robert.Cohen@po-box.esu.edu>wrote:

I've gone back and forth in the past and have now settled on forces first.

In particular, I first examine he difference between forces as
interactions between objects and the "effect" of those interactions (in
terms of changes in motion). Getting students to recognize the difference
is important. I start with Newton's 3rd law.

I don't need to go into detail regarding displacement, velocity and
acceleration. Indeed, I don't introduce the definition of acceleration at
all until after I have finished with displacement and 2-D motion.

The main reason I do this is because my students have trouble with ratios,
so starting with rates of change and graphs just overwhelms them. Starting
with forces first focuses attention on a single main idea (in this case,
that changes in motion are associated with unbalanced forces).

I use my own book for this, which helps.

------------------------------------------------------
Robert A. Cohen, Department of Physics, East Stroudsburg University
East Stroudsburg, PA 18301
________________________________________
From: Phys-l [phys-l-bounces@phys-l.org] on behalf of Bill Nettles [
bnettles@uu.edu]
Sent: Tuesday, March 18, 2014 6:31 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Sequence

I hope this is AFTER you teach them to do unit conversions well.

I like teaching vector algebra first. Even in two dimensions. Of course,
in 9th grade you haven't taught trig to them, have you? If you do
kinematics without talking about vectors I believe they are going to
develop some bad concepts.

Forces are a good way to introduce vectors early.

I'm trying Jeffrey Schnick's approach this year (editing and converting to
LaTeX as I go), and I like it. You have to introduce some quantities by
fiat: K=1/2 m v^2, U_g=mgy, etc. but you can do some applicable
calculations. But kinematics without vector concepts...yech.

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of James
Cibulka
Sent: Tuesday, March 18, 2014 3:00 PM
To: phys-l@phys-l.org
Subject: [Phys-L] Sequence

Good day all!

Several teachers at my school have decided they want to teach forces
first in
our ninth grade physics course.
I currently teach constant velocity, balanced forces, constant
acceleration,
constant net force, energy and finally mechanical waves. One teacher does
motion then forces, and another does forces first, then motion.

We are being told to show up with our arguments why we should follow a
certain sequence. All the headache of college teaching with none of the
joy
it seems!
Anyone here have an opinion on sequence? I'd love to hear from you!

Jim Cibulka
Kirkwood high school
_______________________________________________
Forum for Physics Educators
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_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org
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_______________________________________________
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