Re: [Phys-L] Sequence

[Robert Cohen <Robert.Cohen@po-box.esu.edu>]

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
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