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# Re: [Phys-L] Sequence

Hi June,

Welcome to posting on PHYS-L , the more the merrier. (Though a thick skin helps at times.)

Joel Rauber

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of June Nicholas
Sent: Thursday, March 20, 2014 9:41 AM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Sequence

Hello all,

Surprised no one mentioned Chabay/Sherwood - they teach momentum first.  I'm raising it here for a discussion point!

Not sure I agree with all of their approaches.  Though I love more utilization of time diagrams to connect to their math courses right off, and have tried to do more in recent years.

Also much emphasis on the Third Law.

Interestingly, a HS I taught at decided a few years ago to flip the order of instruction where "second semester" content was covered in the first semester and vice versa, on the proposition that it would make the math easier.  I dissented, of course (one of many reasons I no longer teach there!).

Here is  a follow-up question:

I would teach all straight-line (including 2D or 3D and projectile) motion first, from kinematics to energy.  Then I would teach circular and rotational motion, as (in my opinion) the essential vocabulary and concepts had been introduced.

However, a lot of textbooks include circular motion as part of the early chapters.

Any thoughts?  I welcome all!

From June Nicholas
A first-time poster and former HS and TYC instructor who hopes to do more soon

On Thursday, March 20, 2014 10:17 AM, Philip Keller <pkeller@holmdelschools.org> wrote:

If I were going to try this approach, I would in fact limit motion to
positive velocities.  I see the appeal of forces before kinematics.
But I want to be able to refer to constant velocity vs constant
acceleration as I teach about forces.  So I would leave this nit
unpicked until I came back to kinematics later.

On Thu, Mar 20, 2014 at 9:31 AM, Rauber, Joel <Joel.Rauber@sdstate.edu>wrote:

One nit to pick.

Phillip K wrote in part:

But what if the ONLY things you wanted to get across were:

PART I -- here is one kind of motion we care about.
1.  When an object moves at a constant speed in a straight line, its
position graph is a line.
2.  In that case, the slope of that line stays constant.  That slope
is the speed.
3.  Since the speed is not changing, the "velocity" graph is a
horizontal line.

[:]
[:]
The slope is the velocity not the speed.  If the object were moving
at a constant speed in the opposite direction the slope would be
a 1D situation (which I'm assuming is what is happening here).
Unless you only allow objects to move in the positive direction of
how you oriented your coordinate axis.
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