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

[John Clement <clement@HAL-PC.ORG>]

> I have found that my HS students have a pretty good
> sense of negation, and that when a negative sign is
> placed before the word "acceleration" they (and I) can
> do without the word "deceleration".  We just say that
> the acceleration is negative sometimes.
>
> I prefer to not introduce new vocabulary when existing
> terms suffice.  There are already a lot of new terms
> in an introductory class.
>
> Matt Jusinski  Morris Knolls HS  Rockaway, NJ

But again this reveals a possible misconception in the making.  Negative
acceleration is NOT slowing down or deceleration.  Negative acceleration can
be either slowing down or speeding up depending on the sign of the velocity.
To avoid this very common misconception you have to be very careful, and
have the students do the appropriate labs which dispel it.

Unfortunately just changing a term only gets rid of 1 misconception attached
to that term, while it does little for the many other misconceptions.

I also doubt that most HS students really have a good sense of what negative
means.  They will tell you that when a velocity is decreasing from 40m/s to
30m/s that the change in velocity is 10m/s.  They do not associate the sign
very well with the idea of change in a quantity.  Basically they are
programmed to subtract the second number from the first one just as they did
in grade school, or worse yet always subtracting the smaller number from the
larger one.

John M. Clement
Houston, TX

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