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On 11/09/2010 10:10 AM, William Robertson wrote:
At some point, we have to help people understand physics by using
consistent terms (I failed at that in my use of speed and velocity)
and not saying gosh, golly, gee it's okay for people to use different
language because well, you know, they're really not wrong historically
or some other way. What might be a minor difference in wording to a
physicist who can "get through" that to the heart of the matter,
becomes a major stumbling block for many.
I agree that we shouldn't let the inmates run the asylum,
and that we should clearly delineate new technical terms
from old and/or nontechnical terms.
I'm just saying that when we delineate these things, we
should delineate them *clearly* ... and in particular we
should (in most cases) say what makes the new idea different
from the old idea.
Giving the old idea a name ("scalar acceleration") helps
clarify how the new idea ("vector acceleration") is different.
I find it unhelpful to pretend that the old idea does not
exist, or even to pretend that it is worthless. I prefer
to put the old idea into a sharply delineated box and say
it is not what we wish to talk about today. In favorable
cases, the old idea becomes a stepping stone rather than
a stumbling block.
Speed exists. Speed is |v|. It's just not what we want
to talk about today. Deceleration exists. Deceleration
means (d/dt) speed is less than zero. That's another
thing we don't want to talk about today. We choose this
because physics is simpler in terms of v rather than |v|.
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