Re: speed and velocity

[Bob Sciamanda <trebor@VELOCITY.NET>]

-----Original Message-----
From: Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>
To: PHYS-L@LISTS.NAU.EDU <PHYS-L@LISTS.NAU.EDU>
Date: Wednesday, November 25, 1998 1:01 PM
Subject: Re: speed and velocity
> Positive and negative components of accelerations give my students
> more trouble than problems related to signs of velocity components.
> A v component is positive if an object moves along the axis and
> negative otherwise. But for accelerations it is "sometimes one way
> and sometimes another", even in one dimension.

Yes, the sign of a one dimensional acceleration vector is always a
problem to intro students.  I find that you have to get them to DRAW both
"before" and "after" velocity vectors and GRAPHICALLY subtract them to
SEE the direction of the vector dV;   ie  what vector dV has to be added
to the vector v1 to get the vector v2?
Then a = dv/dt .

Bob Sciamanda
Physics, Edinboro Univ of PA (ret)
trebor@velocity.net
http://www.velocity.net/~trebor