Re: [Phys-l] g...

[Hugh Haskell <hhaskell@mindspring.com>]

At 16:43  -0600 11/18/06, Paul Lulai wrote:
> If you are talking to high school kids (and perhaps college 
> freshman).   Average high school kids... refering to a_g as a 
> measure of field strength or the F/m ratio is a death-blow. 
> They have not been *exposed* to fields.  They are discussing 
> acceleration quantitatively for, perhaps, the first time EVER. 
> They have not really discussed what a force is. 
> They don't *know* the difference between an object's weight and its mass. 
> Telling them it is the ratio of F/m, or a measure of field strength 
> on a first run through is telling them that "a_g is something that 
> they can not understand right now.  Not really." 
I disagree that it is inappropriate or HS students to introduce them 
to fields at this point. If you are doing acceleration early on in 
your course, then perhaps, but we hold off on acceleration until 
after introducing Newton's laws, where acceleration comes in rather 
naturally. By that time, they are ready for some abstraction, and 
fields have to be introduced at some point, so why not here. It isn't 
going to get any easier by the time you get to electricity, and if 
you wait until then, you miss the opportunity to bring in a very 
illuminating and unifying concept.

Calling g, and acceleration, or even dressing it up with the new 
symbol a_g, isn't going to solve the problem, IMO. The point is, that 
g is *not* and acceleration. It happens to have the units of 
acceleration because of an "accident" but that is really irrelevant 
to the physics. It also makes it easier to understand why all object 
accelerate the same way under the influence of gravity alone, whereas 
the same is most definitely not true with electricity.

It seems to me that if we don't keep reminding them that physics is 
based on only a few principles, they will get the idea that there is 
a semi-infinite number of "rules" that they have to memorize in order 
to do anything in physics. This is a golden opportunity to emphasize 
the unity of physics, and show how that unity gets applied under 
slightly different conditions.

Hugh
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Hugh Haskell
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<mailto:hhaskell@mindspring.com>

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When you are arguing with a stupid person, it is a good idea to make sure that
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					Anonymous