Re: [Phys-l] Mass and Energy

[Hugh Haskell <hhaskell@mindspring.com>]

At 08:50  -0700 5/25/06, John Mallinckrodt wrote:
> In my opinion the consistent use of SI units in introductory physics 
> courses only exacerbates the problems students have with units, 
> problems that they WILL face in the cruel world, not to mention our 
> own introductory laboratories. (Does anyone really conduct 
> introductory laboratories in such a way that students never have to 
> face unit conversions??)  Far better to make sure that they 
> understand that units are NEVER to be taken for granted and that 
> unit  conversions are ALWAYS trivial--a little tedious perhaps, but 
> always trivial.)
Yes, they will always be faced with unit issues in the real world, 
but when they are new to the game, unit conversions, no matter that 
they are always trivial, are very confusing to them, and IMO, having 
to worry about them seriously gets in the way of their understanding 
the physics. I grew up in the era when the textbooks spent a whole 
lot of time mixing up units. I remember having to try to sort out 
pounds, poundals, slugs, pounds-force, pounds-mass, Newtons, dynes, 
kg-force, kg-mass, and on and on, and I spend most of my first year 
in physics thoroughly confused, not about what units to use in any 
given situation but how to convert between them. And I won't even 
mention the mess that was electromagnetic units in the days before SI 
became predominant.

When I started teaching, I quickly found that, even though we were 
using SI almost exclusively, units still were a barrier to 
understanding, and they spent more time worrying about which units to 
use where than they did trying to figure out what was going on. So I 
decided to simply remove that impediment from the playing field and 
always use strictly SI units, at least for the first semester. They 
spent a lot of time in chemistry classes worrying about unit 
conversions, so I figured that I would leave that to the chemists, 
since they seemed to enjoy that sort of thing. When I did, I found 
that understanding seemed to come quicker, and once they understood 
what was going on, the unit problems pretty much went away. When they 
were able to concentrate on learning physics, without having to mess 
with unit conversions, it got easier, and when they later ahd to face 
problems with unit conversions, they didn't seem nearly so difficult 
to them, and they were able to incorporate them with only minimal 
effort.

I think that trying to teach too many concepts at once tend to 
overload the students at a point where they can least handle it--kind 
of like trying to teach a student driver to steer the car and work a 
clutch-gear shift at the same time. That's the way I learned, and I'm 
lucky that I only sideswiped one parked car while trying to steer and 
shift at the same time. My kids both learned on automatic shift cars, 
and later I was able to teach them how to use a stick-shift in about 
an hour.

Hugh
--

Hugh Haskell
<mailto:haskell@ncssm.edu>
<mailto:hhaskell@mindspring.com>

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