Re: Newton's 3rd law? was Re: inertial forces (definition)

[Joel Rauber <Joel_Rauber@SDSTATE.EDU>]

Robert Cohen wrote in part:

. . .
> that you would bother to resolve these forces into
> components which are parallel to the velocity vector and perpendicular
> to the velocity vector...and then to identify the net perpendicular
> component with a special name?
> I suggest there is little or no analytical value in doing this,
<snip>
> Someone has probably said this, but I favor talking about radial and
> tangential components of the acceleration, and considering the
> centripetal force as a special case for special circumstances.

It seems to me that you see significant analytical value in doing the above,
you just prefer to call it the net tangential and radial components rather
than the net perpendicular and parallel components.

I view the following as synonyms.

perpendicular component = radial component = transverse component

(I don't really like "radial component" because one doesn't necessarily mean
plane/spherical polar coordinate radial component; but rather component
parallel to the instantaneous radius of curvature.)

tangential component = parallel component

(parallel to what, the instantaneous velocity, of course)

Also, Michael wrote:

> The same is true for the centrifugal force.  In my class, I prefer that
> students use "force directed toward the center" and "force directed away
> from the center" for centripetal force and centrifugal force.  Then, when
> I ask which force is directed toward the center of the motion, I am less
> likely to get the "force directed toward the center" as the answer.

Leigh, agreed with this statement.  I like it too, but would prefer using
the adjective "net" in front of the word "force", so that we would be
talking about the "net force" directed toward the center; etc.

Leigh also asked?
How do you protect
your students from the bad influence of textbooks?

Good question, I want to know what others say or do, including Leigh.  I try
to point out such bad influences, but my students mostly look at me like I'm
crazy for daring to say something in a textbook should be different.

Joel