Re: speed and velocity

[Mervin Koehlinger <tchkoehlimw@CRF.CUIS.EDU>]

On Wed, 25 Nov 1998, Ludwik Kowalski wrote:

> 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.

If I understand what you're saying, I have to disagree with you.  Positive
and negative acceleration refers simply to direction, not whether the
object is speeding up or slowing down. If an object is traveling in the
positive direction and is slowing down that is negative acceleration. If
an object is traveling in the negative direction and is speeding up, that
is also negative acceleration.

In general, if the acceleration is positive, the velocity vector is
becoming more positive.  If the acceleration is negative, the velocity
vector is becoming more negative.

Mervin Koehlinger
Physics Instructor
Concordia Lutheran High School
Fort Wayne, Indiana