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Re: weight of a bird in a cage



We must have two different types of hour glasses. Ours, when totally
inverted, let the sand flow through the neck, after which the sand was
not in contact with the glass at all.

Peter Schoch


Lois Breur Krause wrote:

no. the sand is always resting against the glass of the hourglass and is
therefore supported physically by the system. the fly, when hovering, is
not resting against the structure of the cage, nor is it supported by the
system.

My students, prompted by the "Flying Circus of Physics", tried a
different tack -- one that circumvents the need for the fly.

We took an "hour glass" and weighed it with the sand in the bottom. We
then turned it on its side and reweighed it, with very little sand
moving about. Then, we turned it over (sand on top and flowing into the
bottom chamber) and weighed it.

We did get some fluctuations, above and below the first measured value.
However, it was the opinion of the students after statistical analysis
that the "error" in the electronic balance could account for the
fluctuations, and that no difference was found.

Could I have someone else's opinion? Can't this, indeed, be used to
solve this problem via analogy?
Peter Schoch
Sussex County Community College
pschoch@nac.net



Mark Sylvester wrote:

At 18:19 05-09-99 -0500, brian whatcott wrote:
Ludwik and Mark had a question about a crucial experiment of the
'bird in a box' variety that Jim described. (Quoted below)

The purpose of Jim's description was to demonstrate that the
weight of a box plus flying animal is unchanging, momentary
excursions excepted.

The problem with Ludwik's query, is that it asks if the box
+ animal weight remains constant plus or minus the animal's weight.

The answer to which is "Yes of course, whether it decides in favor
or against either of the following positions":

"the flying animal's weight reacts on the floor" OR
"The flying animal's weight is NOT reacted on the floor".

Hence, I deduce that Ludwik's question went unanswered because
an answer to his question would not contribute anything meaningful
to the discussion.

I am quite certain that this is not the response Ludwik meant
to invoke. But I cannot read his mind, only his words.


snipping the rest of Brian's enigmatic speculations, let me clarify.

Jim Ealy wrote:

Listmembers;

My nature always says go to the lab when I hear "opinions" (I know that
places me several rungs down THE ladder)

My high school students several years ago made a box from dry-cleaner's
plastic wrap and balsa - total was less than 20 grams about 50 cm by 50
cm. A closed system sealed with tape, after fly was inserted - positive
pressure. We waited until spring to capture one of those large flies
(commonly called - casement flies) that emerge in rooms. They placed the
fly in the "box" and placed it on a top-loading balance: 0.1 mg.

*What* weighed 0.1 mg? The fly? Are there really 10 million *big* flies in a
kg?
This struck me as surprising, so I question what exactly the sentence means.

There is
no question about what happens (flying,landing, starting off from bottom
or side or top (or repeating after punching holes in plastic for air to
move in or out as in an open system)).

But what happens - is it that the reading never varies (momentarily) by more
than 0.1 mg?

Brian points out that Ludwik screwed up his question (and I didn't read it
carefully enough), but I really would like to know what Jim meant. Maybe
I'll just catch some flies and weigh them....

Mark

Mark Sylvester
United World College of the Adriatic
34013 Duino TS
Italy
msylvest@spin.it