Barometer question
The barometer question is a well-known urban legend in academia. It has multiple forms, but all are based on the same premise: an examination paper in Physics which includes the question, "How would you measure the height of a tall building using an aneroid barometer?" There has never been any confirmed record of this question having appeared in an exam paper.
The presumed intended answer is that it could be done by comparing the barometer readings at the top and bottom of the building; however, the urban legend is based on a student - or several students - giving other answers which are completely correct but not the intended one. Example answers include:
- Tying the barometer to the end of a piece of string, lowering the barometer from the top of the building and then measuring the length of the string and barometer once the barometer touches the ground (some say this answer was provided by a young Niels Bohr);
- Lowering the barometer from the top of the building on a piece of string, then swinging it like a pendulum and measuring the period of its oscillation;
- Using a shorter piece of string measure the period of the makeshift pendulum at the top and bottom of the building. Use the two values to determine the change in gravitational force and therefore the height of the building;
- Dropping the barometer off the top of the building, using a stopwatch to measure how long it takes to hit the ground, and solving for height in the equations for a falling body;
- Measuring the barometer, then placing the barometer against the building, marking the top, placing the barometer above the mark, marking the new top, and so on until the building has been measured in "barometers";
- Measuring the barometer, finding the length of the shadow cast by the barometer when stood on the ground, then finding the length of the building's shadow in the same conditions;
- Finding the building custodian and offering them the barometer in exchange for information about the height of the building.
In different versions of the legend, the student is passed for their answer, or initially failed but then passed after protest, or similar.
It might seem that all of these supposed solutions, except for the last one, require the person to possess another method of measurement other than the barometer. (For example, measuring the length of the string and barometer requires another method of measuring length.) However, since the question does not specify the units required, one could use the length of the barometer itself to measure the length of the string, etc. and give results in "barometers". This is no different from using any other agreed-upon standard, such as a yardstick.
Asking the custodian is thought by purists to be invalid, since at no point is a measurement made. Some people avoid this caveat by changing the question to 'How would you determine the height of a building?'.
Popular Culture
A version of the barometer question features in Terry Pratchett's novel Strata.