> > Great Moments in Physics

> >

> > The following 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. The student 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 a 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 sqroot (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 person from Denmark

> > to win the Nobel prize for Physics.

> >