Re: point particles

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

I wrote:

> In the case under consideration ... no "riding" is actually
> required.  I simply ask you to consider the motion of a rod with a
> UNIFORM mass distribution and positive electric charge at ONE end
> subject to oppositely directed and uniform gravitational and
> electric fields with mg = qE.

To which Bob wrote:

> If mg=qE the net force is zero, the CM remains at rest, and so you ARE
> riding it  ;>)

True enough and perhaps sufficient "explanation" for those for whom
the mathematics IS intuition.

But as a final attempt to put perhaps too fine a point on it,
consider the rod I described held horizontally in front of you.  Now
simply let it go.  What does your intuition tell you it should do?

I can explain why it does what it does in terms of Newton's laws, but
it still really bothers me!

--
John Mallinckrodt        mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm