This is for Loring

[BobSch]

Sir Ernest Rutherford, President of the Royal Academy, and recipient of the Nobel Prize in Physics, related the following story:

"Some time ago I received a call from a colleague. He was about to give a student a zero for his answer to a physics question, while the student claimed a perfect score. The instructor and the student agreed to an impartial arbiter, and I was selected.

I 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 it 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."

The student really had a strong case for full credit since he had really answered the question completely and correctly! On the other hand, if full credit were given, it could well contribute to a high grade in his physics course and certify competence in physics, but the answer did not confirm this. I suggested that the student have another try. I gave the student six minutes to answer the question with the warning that the answer should show some knowledge of physics.

At the end of five minutes, he hadn't written anything. I asked if he wished to give up, but he said he had many answers to this problem; he was just thinking of the best one. I excused myself for interrupting him and asked him to please go on. 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 x=0.5*a*t^2, calculate the height of the building."

At this point, I asked my colleague if he would give up. He conceded, and gave the student almost full credit. While leaving my colleague's office, I recalled that the student had said that he had other answers to the problem, so I asked him what they were.

"Well," said the student, "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 simple proportion, determine the height of the building."

"Fine," I said, "and others?"

"Yes," said the student, "there is a very basic measurement method you will like. In this method, you 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 his will give you the height of the building in barometer units."

"A very direct method."

"Of course. If you want a more sophisticated method, you can tie the barometer to the end of a string, swing it as a pendulum, and determine the value of g [gravity] at the street level and at the top of the building.

From the difference between the two values of g, the height of the building, in principle, can be calculated."

"On this same tack, you could take the barometer to the top of the building, attach a long rope to it, lower it to just above the street, and then swing it as a pendulum. You could then calculate the height of the building by the period of the precession".

"Finally," he concluded, "there are many other ways of solving the problem."

"Probably the best," he said, "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 is a fine barometer. If you will tell me the height of the building, I will give you this barometer."

At this point, I asked the student if he really did not know the conventional answer to this question. He admitted that he did, but said that he was fed up with high school and college instructors trying to teach him how to think.

The name of the student was Neils Bohr.

[windmill]

Priceless.

[cabinetman]

I like the first and last answer.
.

[Norm in Fujino]

That's the difference between conventional intelligence and genius

[woodturner]

The name of the student was Neils Bohr.

Who, some may recall, developed the model of the atom that held for many, many years, and is still taught in some high schools (even though it has been superceded by a better model).

I'm guessing most of us think of the atom in the context of the Bohr model - valence bands surrounding a nucleus.

[chopnhack]

Great story, I love how he was fed up back then with how schools teach! Does anyone know the "conventional" answer the teacher was looking for? Was it simply subtracting sea level pressure from a know height's pressure and then relating that to the pressure measured at the top of the building? Something else?

[BigguyZ]

I'm curious- is that a true story?

[os1kne]

It's a great story, and both men are geniuses - but I don't think that they were in the same place at the same time during the stage of Bohr's education when he would have faced a question of that nature.

http://www.bbc.co.uk/history/histori...d_ernest.shtml

http://micro.magnet.fsu.edu/optics/t...ople/bohr.html

[LCHIEN]

I would not have chosen the first answer, too much rope and too slow.
I would have chosen the second, that was my second thought (throwing the barometer off the building and timing the fall); it would have required the least amount of effort (e.g. only one trip up the building whereas most of the other answers required at least one or more trips) and elapsed time.

However, I fault the original professor for not specifying the precision with which he wanted the answer. I am an engineer; I use scientific principles to slelect the best solution that fits the specification (e.g want an answer fast or want it accurate or expend the least effort).

The other assumption of course is the the original professor wanted an answer utilizing the special property of the item specified in which case using the differential pressure to indicate the height is the correct answer. Most of the other methods require ancillary items (rope, string, ruler to measure the height of the barometer and/or rope, stopwatch etc) or measuring devices, only the barometer is useful in and of itself because it is a measuring device. It's still arguable that the differential pressure method requires knowledge of the weight of a column of air, in which case bribing the super is the only correct answer that does not require other knowledge or tools.

[vaking]

The student failed the test. "A barometer is a scientific instrument used to measure atmospheric pressure" (Wiki). The definition does not specify device construction or physical properties. While most actual barometers have dial - there are other types, such as 10 meter long pipe with water. Every solution offered by the student made assumption about physical properties of barometer and would have worked equally well if barometer was replaced with a clock of comparable size. It would have worked much worse, however, if barometer was of a different kind. I'd like to see anybody swing 10 meter long water pipe on the rope. Not a single solution measured atmosperic pressure. It means student offered multiple solutions all utilizing device of specific physical properties but not barometer. Question was not answered.
Students sometimes resent that they are being taught to think but this specific student did need to learn that thinking begins with analysis of a question and with definitions. I don't think the case was real, Neils Bohr was not like it.

[BobSch]

I'm curious- is that a true story?

Snopes call it a legend but I like the idea that there's often more than one answer to a question.

http://www.snopes.com/college/exam/barometer.asp

[jackellis]

It's very easy to get stuck in a rut when it comes to problem solving. Even very smart people often search for solutions to problems by using multiple incremental approaches over time when there's a more direct way that involves casting aside a few preconceived and outdated ideas.

I see this a lot in my industry, where there's great reluctance to consider other than incremental approaches to difficult problems.

[LCHIEN]

It's very easy to get stuck in a rut when it comes to problem solving. Even very smart people often search for solutions to problems by using multiple incremental approaches over time when there's a more direct way that involves casting aside a few preconceived and outdated ideas.

I see this a lot in my industry, where there's great reluctance to consider other than incremental approaches to difficult problems.

people in search of the most straightforward solution tend to use solutions for which they already have the resources and knowledge.

Case in point, check out my Sig line!

VAKing: The original professor did not specify a precision or error tolerance to which he wanted the answer. Hence the relative size of the barometer in proprotion to the measurement errors should not be held against him. Every one who has taken Physics in college should have learned that an answer is not an answer without error bars. So an answer of 200 feet plus or minus 30 feet should be a perfectly acceptable answer to the question of determine the height of the building, if not given specific error boundaries to meet.

[radhak]

The student failed the test. .... Not a single solution measured atmosperic pressure. It means student offered multiple solutions all utilizing device of specific physical properties but not barometer. Question was not answered.

If the question was what is stated, then the student cannot be penalised - it did not say 'use atmospheric pressure', so the barometer could be used for anything. To allow for that, imagine the object handed over was a rubber ball, and no other instruction. What would you think was the intent behind the question - use it as a pendulum? Or throw it down to measure the time it takes to fall?

On the other hand, it takes a gutsy (foolhardy) student to take on an instructor in this fashion. I sorta regret that I was never able to do that, but have seen friends who'd push the envelope pretty far - there was this time a paper said, "Please choose one these three theorems to solve", and a classmate's answer was simply - "I choose the 2nd theorem", but he never bothered to solve it . It spiraled into a battle between him and the professor, which he lost, but it was fun to watch .

The OT is surely not a true incident, and definitely not related to Bohr. Looks like it was a collection by some professor of answers by various students. It still makes very interesting reading. I should try it on my brother-in-law...

[BobSch]

I certainly didn't expect so many responses to my post. Maybe I should post the question as to whether H#ll is exothermic (gives off heat) or endothermic (absorbs heat).