Re: [Phys-l] Deceleration or Negative Acceleration

[Herbert Schulz <herbs@wideopenwest.com>]

On Sep 9, 2008, at 10:33 AM, Joseph Bellina wrote:

> I think there may be another issue here.  Some motion variables are
> scalars, like distance and speed, others are vectors like
> displacement and velocity.  Acceleration is ambiguous, which can be a
> problem.  Perhaps the word deceleration suggests a scalar concept,
> whereas negative acceleration is the vector concept.
>
> joe
>
> Joseph J. Bellina, Jr. Ph.D.
> Professor of Physics
> Saint Mary's College
> Notre Dame, IN 46556
>
> On Sep 9, 2008, at 10:02 AM, pschoch@nac.net wrote:
>
> > I instituted the use of "Reading Questions" in my classes this
> > year, and I
> > am getting some of the most interesting questions this semester
> > from my
> > students.
> >
> > This is one that I've not run into before...  A student has asked
> > which is
> > proper terminology:  "Negative Acceleration" or "Deceleration".
> >
> > Of the textbooks on my shelf, about half are for the first and the
> > other
> > half seem to use both interchangeably.  Interestingly, those that say
> > "Negative Acceleration" is the proper term are all of a more recent
> > vintage.
> >
> > Is one or the other really more used/acceptable?
> >
> > Thanks,
> > Peter


Howdy,

Acceleration is a vector quantity.

One really shouldn't think in terms of sign since you are free to  
choose any coordinate system. A deceleration will occur whenever the  
acceleration (has a component) that is opposite to the direction of  
the velocity vector. If a given component of the velocity vector and a  
corresponding component of the acceleration vector have opposite signs  
there will be a deceleration along that direction.

Good Luck,

Herb Schulz
(herbs@wideopenwest.com)