falling pie plate (was: ... *earth* vs. *wing*)

["Carl E. Mungan" <cmungan@UWF.EDU>]

Ludwik Kowalski wrote about a pie plate falling inside a closed cage:

> Hmmm, but it keeps compressing air and pushing it toward the scale.

Then William Beaty replied:

> Yes, but only when it is fairly close to the bottom.

So I say:

I thought this was settled when I asked about the bird hovering in the cage
and the standard answer was cogently stated (by some list member whose name
I've forgotten - sorry).

With the bird hovering, the scale reads the same as with the bird resting
on the bottom as we see from a simple center-of-mass argument. There is no
reference here to how high the bird is above the bottom of the cage.

Beaty (or should I say William or Bill - what is correct etiquette?)
appears to have a model in mind that the air forms closed loops going down
from the bird, out, back up, passing the bird, and finally turning back in
and down to the bird. Please correct me if I'm misrepresenting your views.

If it is, I'd say the bird (plane, pie plate, whatever) is holding himself
up by his own bootstraps!

Carl
ps: Please excuse the considerable delays in keeping up with the list. I
only read digests and only when I find the time. (How do some of you very
active list members - like Beaty - find the time to do anything else but
read & write on list matters?)

Dr. Carl E. Mungan, Assistant Professor     http://www.uwf.edu/~cmungan/
Dept. of Physics, University of West Florida, Pensacola, FL   32514-5751
office: 850-474-2645 (secretary -2267, FAX -3323) email: cmungan@uwf.edu