At last, the field of physics has its own version of the urban legend

Image for article titled At last, the field of physics has its own version of the urban legend

Ever heard the one about the barometer? It's a famous physics urban legend that has been attributed to everyone from a cheeky student at MIT to Niels Bohr himself. It's about creativity, problem solving ability, and good, old-fashioned sass. You decide whether it actually really happened!


It goes like this:

An instructor administering an exam to his students asks them to measure the height of a building using a barometer. A students turns in a paper which says, "Tie a string to the barometer, lower it down the side of the building, and measure the string." The instructor is furious and fails the student. The student appeals the decision, stating that he gave a correct answer. The committee decides that, yes, the answer was correct, but the student did not show any understanding of physics so it is inadmissible. They will give the student one more chance to answer, but he will have to demonstrate a knowledge of physics to pass. The student sits there thinking. When the examiners ask him if he gives up, he says that there are so many answers that, by golly, he just can't pick one. They tell him that they'll fail him unless he says something. He says this:

You can measure the shadow and the length of the barometer, and then measure the shadow of the building, and use the ratio of shadow-to-length to figure out the height of the building.

You can just drop the barometer over the side of the building and figure out the height by the time it takes to hit the ground.

You can make a pendulum from the barometer and measure the gravitational force exerted by measuring the swing, calculate the force of Earth's gravity, which lessens as you get away from the Earth, thus determining the height of the building.

You can climb down the fire escape, using the barometer as a ruler, and mark off the building's height in barometer lengths.

If you're very dull, you can use the barometer to calculate the air pressure on the ground and at the top of the building and use the difference to work out the height of the building.

Or if you're smart, you can go to the janitor and tell him that you'll give him this beautiful new barometer if he tells you the height of the building.

This old chestnut has been chalked up to every clever student ever to study physics. The most popular incarnation of the legend attributes it to Niels Bohr, brilliant physicist and Nobel Laureate. Still, the first written version of the story only goes back to 1958 - considerably after Bohr's student years - and was written by Alexander Clanadra, in a textbook about encouraging students to think of all the ways to solve a problem. He does say it was a true account of a real student, but that student - with nerves of steel - has not been identified.

Know anyone you think might say something like that? Maybe your friend's cousin's friend?

Top Image: Bob Jagendorf

Via Snopes and Haverford.




A much more extensive list of "ways to measure the height of a building using a barometer" may be found here: