Re: Derivations

[Hugh Haskell <hhaskell@MINDSPRING.COM>]

>  >I'm not a stuffy about derivations for the following reasons: first,
> > I remember how much trouble I had with them as a student, usually
> > ending up just memorizing them.
>
> It is not clear to me just what this thread re derivations is all
> about.  Just which derivations are being done or not done here?  Are we
> talking about Newton, Kirchoff, Faraday, Maxwell, Einstein?  What is so
> difficult to talk about in a discussion and maybe a few scratches on the
> board??
>
> The idea of work absolutely must be derived but that takes only two lines
> on the board if they can't see it in their heads with out that.  OK maybe a
> few lines for rotational dynamics.  A few lines for vectors.  What is so
> problematic???
>
>
> Jim Green

I think you're being optimistic, Jim. I'm not talking about deriving
Maxwell's equations, or the Lorentz transformation. We don't deal
with those in a first-year HS course. I'm talking about students who
are still getting their sea-legs in the ocean of algebra. they have
trouble with the three kinematics equations (at^2/2, and all that).
Center of mass motion is a real stretch for them. We do most of the
relativistic equations, but from a geometric point of view, and most
of the students are dizzy by the time we finish with them. There are
not dumb kids, but they are not used to dealing with this kind of
reasoning and they have to be led into it gently. They could memorize
the derivations, and would if I asked them to, but what would be
gained by asking them to reproduce, say the geometric derivation of
the time-dilation equation, after I have done it in detail in class?
That is little more that factual recall that they will forget the day
after the test.

My point was this. It is important for them to see the derivations of
everything they can possibly understand. Even if they don't
understand what I did, and can't short of rote memorization,
reproduce it. They need to understand that physics is a serial topic
where each level is built on the previous one and that there is a
logical thread that holds it all together. Most of these kids will
not study any more physics, so it is not important that they learn
how to do the derivations, but it is critical that they understand
what we mean when we say that physics is no more a pile of facts than
a house is a pile of stones.

Hugh
--

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

Let's face it. People use a Mac because they want to, Windows because they
have to..
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