Courage Lives On {Insp}

"Courage Lives On"*
*
This legend, the truth of which is not necessarily
related to its value, concerns a question in a
physics degree exam at the University of
Copenhagen: "Describe how to determine the
height of a skyscraper with a barometer."
 
One student replied: "You tie a long piece of string
to the neck of the barometer, then lower the
barometer from the roof of the skyscraper to the
ground. The length of the string plus the length of
the barometer will equal the height of the building."
 
This highly original answer so incensed the
examiner that the student was failed immediately.
 
He appealed on the grounds that his answer was
indisputably correct, and the university appointed
an independent arbiter to decide the case. The
arbiter judged that the answer was indeed correct,
but did not display any noticeable knowledge of physics.
 
To resolve the problem it was decided to call the
student in and allow him six minutes in which to
provide a verbal answer which showed at least a
minimal familiarity with the basic principles of physics.
 
For five minutes the student sat in silence, forehead
creased in thought. The arbiter reminded him that
time was running out, to which the student replied
that he had several extremely relevant answers, but
couldn't make up his mind which to use.
 
On being advised to hurry up the student replied as follows:
 
"Firstly, you could take the barometer up to the roof
of the skyscraper, drop it over the edge, and measure
the time it takes to reach the ground. The height of
the building can then be worked out from the formula
H = 0.5g x t squared. But bad luck on the barometer.
 
"Or if the sun is shining you could measure the height
of the barometer, then set it on end and measure the
length of its shadow. Then you measure the length of
the skyscraper's shadow, and thereafter it is simple
matter of proportional arithmetic to work out the
height of the skyscraper.
 
"But if you wanted to be highly scientific about it, you
could tie a short piece of string to the barometer and
swing it like a pendulum, first at ground level and then
on the roof of the skyscraper. The height is worked
out by the difference in the gravitational restoring
force T = 2 pi sq root(l / g).
 
"Or if the skyscraper has an outside emergency staircase,
it would be easier to walk up it and mark off the height
of the skyscraper in barometer lengths, then add them up.
 
"If you merely wanted to be boring and orthodox about
it, of course, you could use the barometer to measure
the air pressure on the roof of the skyscraper and on
the ground, and convert the difference in millibars into
feet to give the height of the building.
 
"But since we are constantly being exhorted to exercise
independence of mind and apply scientific methods,
undoubtedly the best way would be to knock on the
janitor's door and say to him 'If you would like a nice
new barometer, I will give you this one if you tell me
the height of this skyscraper'."
 
The student was Niels Bohr, the only Dane to win the
Nobel prize for Physics.
Received on Sun Sep 21 01:49:09 2008