On 11/19/2003 04:10 PM, Bob LaMontagne wrote:
>
> I would be willing to bet that if you took a biology or chem major
> who has had a year of physics and asked them a couple of years after
> they took the course 'If a ball is thrown upward at 40 m/s, what is
> its speed after 2 seconds?', they will probably get it right. If you
> ask them the acceleration at the peak of the ball's motion, I think
> most of them will say 'zero'. (I bet most of the faculty would too!)
Having put on my flame-retardant suit, let me say that
I don't blame the non-physics-majors! There's not
even any proof that they've got the wrong physics in
mind. Part of it is an issue of terminology more than
anything else. (Of course there may be some admixture
of wrong physics, too.)
In my book, there is such a thing as scalar acceleration
which means an increase in speed (|v|). It is the
opposite of deceleration. This meaning of the word
has been around for centuries and cannot be considered
wrong. Every physicist I know uses the word in this
way some of the time.
Of course there is also such a thing as vector acceleration
which is the quantity that appears in F=ma.
Asking what is "the" acceleration at the peak of a
parabolic arc is at best ambiguous.
-- The scalar acceleration is zero. The speed
is locally constant at this point.
-- The vector acceleration is of course just g.
When I ask somebody an ambiguous question, they get
full marks for answering any reasonable interpretation
of the question. (There is some discretion about what
"reasonable" means; there is the usual continuum:
expected--original--eccentric--smartaleck--perverse.)
Extra points if they detect the ambiguity and deal
with it.