"Describe how to determine the height of a skyscraper using a barometer."

The student replied: "Tie a long piece of string to the barometer, lower it 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 answer so incensed the examiner that the student was failed immediately. However, the student appealed on the grounds that the answer was indisputably correct, and the university appointed an independent arbiter to decide. The arbiter judged that the answer was indeed correct, but that it did not display any noticeable knowledge of physics.

To resolve the problem, it was decided to call the student and allow six minutes for him to provide an oral answer. For five minutes the student sat in silence, his forehead creased in thought. When the arbiter pointed out that time was running out, the student replied that he had several extremely relevant answers but could not decide which to use.

• "Firstly, you could take a barometer up to the roof of the skyscraper, drop it over the edge and measure the time it takes to reach the ground, but too bad for the barometer.
• "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.
• "If you wanted to be highly scientific, you could tie a short piece of string to the barometer and swing it as a pendulum, first at ground level, then on the roof of the skyscraper. The height of the building can be calculated from the difference in the pendulum's period.
• "If the skyscraper has an outside emergency staircase, it would be easy to walk up it and mark off the height in barometer lengths.
• "If you wanted to be boring and orthodox, 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 into a height of air.
• "But since we are continually being urged to seek new ways of doing things, probably the best way would be to knock on the janitor's door and say: "If you would like a nice new barometer, I will give you this one if you tell me the height of this building'."

This story ties in well with an anecdote recounted in Abraham Pais' book Niels Bohr's Times, in Physics, Philosophy and Polity (Oxford, 1991). In his youth, Bohr played goalkeeper in soccer. On one occasion his team was playing against a German side, and most of the action was taking place in the German half of the field. Suddenly the German team counterattacked, and a spectator had to shout to warn Bohr, who was using the goalpost to write down a mathematical problem.
 
 
 

back to Jokes page -- thanks, ~allen, for the Bohr joke!