Supposedly, it was Niels Bohr:
Originally Posted by vtjim
It's like the old joke about the student who was asked how to determine the height of a building. His answer: "Ask the building manager" or something like that.
A student refused to parrot back what he had been taught in class.
When the student protested, I was asked to act as arbiter between
the student and his professor.
I went to my colleague's office and 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 the barometer 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.'
A high grade is supposed to certify competence in physics, but
the answer did not confirm this. I suggested that the student
have another try at answering the question. I gave the student
six minutes, with the warning that his answer should show some
knowledge of physics. 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
S = 1/2at^2, calculate the height of the building.'
At this point, I asked my colleague if he would give up. He
conceded, and I gave the student almost full credit.
In leaving my colleague's office, I recalled that the student
had said he had other answers to the problem, so I asked him what
'Oh, yes. 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 a simple proportion, determine
the height of the building.'
Fine, I said. And the others?
'Yes. 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 this will
give you the height of the building in barometer units. A very
'Finally, there are many other ways of solving the problem.
Proably not the best 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
I have a fine barometer. If you will tell me the height of this
building, I will give you this barometer".'
Other solutions off the net:
Walk away from the building with the barometer at arm's length.
Once the apparent height of the barometer is the same as the
building's, measure the distance from the building and the height
of the baraomter and use a little trig.
Tie the barometer to the end of a long string such that the
end just touches the ground when you hold it from the roof.
Raise it (say) one foot. Swing the barometer-pendulum and
time its period, then calculate the length of the pendulum
from the pendulum equation T = 1/(gL)**0.5 -- don't forget
to add back that foot.
Walk back a measured distance from the building. using any convenient means, throw the barometer at the top of the building. (Use trial and error until you get the aim right) Measure the angle from the ground and the initial velocity, account for wind and air resistance, use several formulae, and be prepared to account for why you just smashed the sh*t out of the professor's new barometer.
Give the barometer to a cab driver in exchange for him taking you over to City Hall so you can look up the height of the building in their records.
Use the barometer to weigh down a piece of string and lower the string down the side of the building. Then you could: a) pull the string up and measure it, or b) start it oscillating like a pendulum, measure the length of a period, and calculate the length of the string from that.