Re: Decceleration and sign of the acceleration componet

[Brian McInnes <bmcinnes@PNC.COM.AU>]

----------
 Ludwik, you wrote near the end of your useful comments on
acceleration and deceleration and signs o velocity and acceleration:
In other words, a component of an acceleration vector is
> positive when its direction coincides with the direction of
> the velocity component. And it is negative otherwise.

I think you meant to write
 a component of an acceleration vector is
> positive when its direction coincides with the direction of
> the displacement component. And it is negative otherwise.


We have a positive acceleration when the velocity component is towards
the origin (negative) and the particle is slowing down.

You also wrote:
> Acceleration and deceleration terms are used in plain English
> as references to opposite things (see also contaminate versus
> decontaminate, activate versus deactivate, etc.), That is the
> source of confusion.

That is certainly getting to the source of the confusion. I prefer to
get students to forsake the use of the (ambiguous) term deceleration
and refer to slowing down or speeding up.

Of course when we work in the observed three dimensional world, we
have the vector equation F = ma and the acceleration is a vector,
neither positive or negative, but in the sam=e direction as the net
force.


Brian McInnes