The barometer

The start of school for many of us inspires me to drag out the famous (to some of us) story of The Barometer.

Miniature barometer next to miniature physics book. Pen for scale.

As the story goes, a physics teacher posed this question on an exam and got surprising results.

Show how it’s possible to determine the height of a tall building with the aid of a barometer.

One student answered this way:

“Take the barometer to the top of the building and attach a long piece of rope to it. Lower the barometer until it hits the sidewalk, then pull it up and measure the length of the rope, which will give you the height of the building.”

What? The teacher expected a different answer, using the standard equation involving the difference in pressure at the top and bottom of the building.

When challenged to come up with “the right answer,” the student gave several more. Among them:

1. 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. Using simple proportion, determine the height of the building.

2. 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.

And so on.

My favorite remains this one:

“Take the barometer to the basement and knock on the superintendent’s door. When the superintendent answers, say: ‘Mr. Superintendent, if you will tell me the height of this building, I will give you this barometer.’”

How would you grade this student?

** Legend has it that the student was Niels Bohr (1885-1962, Nobel Prize in physics, 1922), but then a legend can say anything and get away with it.

 

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