A college professor asked the class how to measure the height of a
skyscraper using a barometer.....
I am reminded of the story about a student who protested when his answer was
marked wrong on a physics test.
In answer to the question, "How could you measure the height of a tall
building, using a barometer?" he was expected to explain that the barometric
pressures at the top and the bottom of the building are different, and by
calculating, he could determine the building's height. Instead, he answered,
"I would tie the barometer to a string, lower it to the ground and measure
the length of the string."
His instructor admitted that the answer was technically correct but did not
demonstrate a knowledge of physics.
The student then rattled off a whole series of answers involving physics -
but not one using the principle in question: He would drop the barometer and
time its fall. He would make a pendulum and time its frequency at the top
and the bottom of the building. He would walk down the stairs marking
"barometer units" on the wall.
"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
"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 sqr root
"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'."
Christopher A. Young
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