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4) "Deceleration" is definitely an odd duck. The problem
is that students tend to assume that a deceleration must
be the opposite of an acceleration.
According to that definition, a deceleration is a special
case of an acceleration. It is !!not!! the opposite of
an acceleration, just as dromedary is not the opposite of
camel. Half of all accelerations are decelerations.
The puzzling thing is that AFAIK there isn't a Latin-based
word for the opposite of deceleration. If somebody can
find/invent one, please let me know!
But if speeding up results from a forward acceleration,
why not just use the obvious corresponding term "slowing
down" for the rearward acceleration? According to my
friends Strunk and White, if you want to communicate
parallel ideas, it is good style to use parallel words.
...
The most important point I'd like to make concerns _my_
speech not students' speech. I have a bad habit of using
"acceleration" and "deceleration" in ways that suggest
they are opposites.
Every time I do that I feel guilty,
because I feel I'm perpetuating a troublesome misconception.