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Re: (dv/dt) terminology: opportunity for improvement



I agree this is confusing, but I am not in favor of new words. Students
who want to understand this can certainly do so. The ones who never
figure it out typically never get other physics concepts figured out
either.

I tell students we will use the words "speeding up" when the magnitude
of velocity is increasing. We will use the words "slowing down" when
the magnitude of velocity is decreasing. I tell students we won't use
the word "deceleration" at all. We will always use the word
"acceleration" in reference to a vector although it is permissible to
speak of the magnitude of the acceleration.

In one-dimensional motion, if the signs of the acceleration and velocity
are the same, the object is speeding up. If the signs of acceleration
and velocity are opposite, the object is slowing down. In the
opposite-sign case (when the object is slowing down), if the
acceleration persists, the object will eventually come to rest
momentarily then the sign of the velocity will switch to the same sign
as the acceleration. Thus, after coming to rest, the object will speed
up in the direction opposite to what it was originally going.

I tell them that outside of physics class they can use deceleration for
slowing down, and they can use acceleration for speeding up, if they
want to. But there is no need to do so; slowing down and speeding up
are fine words.

After we discuss this for a while, most students understand it well. A
few seem to understand but forget it. A few never figure it out. This
is roughly the way it works for all topics, so I don't see a need to
change terminology.

Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Chair of Sciences
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.