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

[Bob Sciamanda <trebor@VELOCITY.NET>]

Let's lighten up!

John, I think you are being too harsh and impolite, or you mis-understand
the man!

Problem solving involves using what is known, to arrive at what is unknown
but calculable.

If I know the radius of curvature and the speed of a particle's present
motion (in a Newtonian inertial frame) then I can take advantage of the
fact that the component of the net force (of the universe) on this
particle, perpendicular to its present velocity direction, is mv^2/r and
is directed toward the center of curvature of its present path.

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, October 21, 1999 4:51 PM
Subject: Re: Newton's 3rd law? was Re: inertial forces (definition)


> > ... Students should be taught to use free object diagrams in both
> > equilibrium and non-equilibrium conditions. Far from being gratuitous,
> > the centripetal force (that is shown in the diagram ONLY when the
object
> > is experiencing an acceleration perpendicular to its velocity) is
> > necessary to justify and explain the non-uniform motion. The student
> > should be taught that the force MUST be there because of the motion;
the
> > task for the student, then, is to discover the source of this force.
>
> To which I, and I think most of us, shout, "Nonsense."  Yes, one *can*
> choose to have students do it this way, but it most certainly is *not*
> necessary.  In my experience most physics teachers find this type of
> instruction to be a most potent source of confusion.
>
> John Mallinckrodt      mailto:ajm@csupomona.edu
> Cal Poly Pomona          http://www.csupomona.edu/~ajm