Re: [Phys-l] Deceleration or Negative Acceleration

["Quist, Oren" <Oren.Quist@SDSTATE.EDU>]

An idea I try to impress upon my students is to draw a sketch and to
choose a coordinate system.  Then the negative acceleration makes sense.

Oren Quist, Ph.D., P.E.
Professor and Head
Department of Physics
South Dakota State University

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Rick
Tarara
Sent: Tuesday, September 09, 2008 9:18 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Deceleration or Negative Acceleration

I don't like either term.  In our usage, accelerations in the direction
of 
motion cause object to increase speed while accelerations opposite the 
direction of motion cause objects to decrease speed.  Accelerations at
right 
angles to the direction of motion cause a change in direction. 
Accelerations at any angles other than 0, 90,180,270 are dealt with by 
breaking the motion into orthogonal components and analyzing the 
accelerations along each of those directions with the above rules.

All of that is a mouthful and requires some considerable effort to
ingrain, 
but it eliminates a lot of other problems, not the least of which is the

freedom to choose positive/negative directions in any particular 
situation/problem.

my 20 ml worth of gasoline!  ;-)

Rick

***************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN
rtarara@saintmarys.edu
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Free Physics Software
PC & Mac
www.saintmarys.edu/~rtarara/software.html
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----- Original Message ----- 
From: <pschoch@nac.net>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Tuesday, September 09, 2008 10:02 AM
Subject: [Phys-l] Deceleration or Negative Acceleration


> 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
>
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