[cdn-nucl-l] EFN - about physics and barometers (fwd)

["S. Mohammad R. Nejat" <nejatsm@mcmail.cis.McMaster.CA>]

I liked this one, you may like it.


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Dear friends of clean nuclear energy,

Please find below a true (?) story about physics and barometers.

With best regards,

Bruno Comby
President of EFN
__________________

EFN's web site :    http://www.ecolo.org
_______________________________________

Sir Ernest Rutherford, President of the Royal Academy, and recipient of
the Nobel Prize in Physics, related the following story: "Some time ago
I
received a call from a colleague.  He was about to give a student a zero

for his answer to a physics question, while the student claimed a
perfect
score.  The instructor and the student agreed to an impartial arbiter,
and I was selected.

I read the examination question: "Show how it is possible to determine
the height of a tall building with the aid of a barometer."

The student had answered: "Take the barometer to the top of the
building,
attach a long rope to it, lower it to the street, and then bring it up,
measuring the length of the rope.  The length of the rope is the height
of the building."

The student really had a strong case for full credit since he had really

answered the question completely and correctly!  On the other hand, if
full credit were given, it could well contribute to a high grade in his
physics course and certify competence in physics, but the answer did not

confirm this. I suggested that the student have another try. I gave the
student six minutes to answer the question with the warning that the
answer should show some knowledge of physics. At the end of five
minutes,
he hadn't written anything.  I asked if he wished to give up, but he
said
he had many answers to this problem; he was just thinking of the best
one. I excused myself for interrupting him and asked him to please go
on. In
the next minute, he dashed off his answer which read:  "Take the
barometer to the top of the building and lean over the edge of the
roof.  Drop the
barometer, timing its fall with a stopwatch.  Then, using the formula
x=0.5*a*t^2, calculate the height of the building."

At this point, I asked my colleague if he would give up.  He conceded,
and gave the student almost full credit. While leaving my colleague's
office,
I recalled that the student had said that he had other answers to the
problem, so I asked him what they were.

"Well," said the student, "there are many ways of getting the height of
a
tall building with the aid of a barometer.  For example, you could take
the barometer out on a sunny day and measure the height of the
barometer,
the length of its shadow, and the length of the shadow of the building,
and by the use of simple proportion, determine the height of the
building."

"Fine," I said, "and others?"

"Yes," said the student, "there is a very basic measurement method you
will like.  In this method, you take the barometer and begin to walk up
the stairs.  As you climb the stairs, you mark off the length of the
barometer along the wall.  You then count the number of marks, and his
will give you the height of the building in barometer units."

"A very direct method."

"Of course. If you want a more sophisticated method, you can tie the
barometer to the end of a string, swing it as a pendulum, and determine
the value of g [gravity] at the street level and at the top of the
building. From the difference between the two values of g, the height of

the building, in principle, can be calculated."

"On this same tack, you could take the barometer to the top of the
building, attach a long rope to it, lower it to just above the street,
and then swing it as a pendulum.  You could then calculate the height of

the building by the period of the precession".

"Finally," he concluded, "there are many other ways of solving the
problem."

"Probably the best," he said, "is to take the barometer to the basement
and knock on the superintendent's door.  When the superintendent
answers,
you speak to him as follows:  'Mr. Superintendent, here is a fine
barometer. If you will tell me the height of the building, I will give
you this barometer."

At this point, I asked the student if he really did not know the
conventional answer to this question. He admitted that he did, but said
that he was fed up with high school and college instructors trying to
teach him how to think.

The name of the student was Neils Bohr."