THE BAROMETER

A miniature physics lesson set up in my office. Pen for scale.

Even though it’s a virtual year, the start of school for many of us inspires me to drag out the famous (to some of us) story of the barometer.

Question on a quiz:

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.

p(h)=p0exp(−mghkBT)

When challenged to come up with “the right answer,” the student gave several. 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: ‘Ms. 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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4 Responses to “THE BAROMETER”

  1. Sheryl Ruzek says:

    These are great! I always appreciate creative efforts to answer exam questions. As a college freshman, I managed to get full credit on a pop quiz for explaining the sacking of Rome despite being behind on my reading. Still makes me chuckle.

  2. Maryellen says:

    I love those creative answers, too. There is always more than one way to figure things out. Different minds can come up with different solutions.

  3. Eileen says:

    Take the barometer to the top of the building and time how long it takes before it hits the ground. Y=1.2gt^s

  4. Jim Brennan says:

    Love giving the barometer to the super.