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Thread ID: 103899	2009-10-10 02:55:00	Interesting	kenj (9738)	PC World Chat

Post ID	Timestamp	Content	User
818893	2009-10-10 02:55:00	I have a feeling this has been posted before?? But, here goes anyway. It made me chuckle. Ken ..."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 IS IT 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 the rope 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 to 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 had not 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 this 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 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 tact, 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 student was Neils Bohr and the arbiter was Ernest Rutherford.	kenj (9738)
818894	2009-10-10 03:07:00	I thought that was fun, kenj = and I speak as someone with no knowledge of physics. (They didn't offer it to girls in my last-century schooldays) So how about one of you knowledgeables telling us what the correct answer should have been?	Laura (43)
818895	2009-10-10 03:38:00	That's a great tale! It's possible to also use Pythagoras with the barometer to measure the height.	bob_doe_nz (92)
818896	2009-10-10 03:40:00	I ain't a knowledgeable, but barometer is an instrument that is capable of measuring the atmospheric pressure. Through the correlation of the change in atmospheric pressure (which can be detected by the barometer) and the change in height, the readings can be used to estimate the altitude. kenj: A BIG BIG BIG thank you for sharing this interesting tale. :thumbs: Cheers :)	Renmoo (66)
818897	2009-10-10 03:49:00	Loved it Ken. But is it true or apocryphal? :rolleyes:	Richard (739)
818898	2009-10-10 03:53:00	For the principle involved for the answer wanted go here:- www.csgnetwork.com	Sweep (90)
818899	2009-10-10 04:00:00	Best post of this year. (Speaking as one who has overhauled/calibrated many altimeters and barometers.)	R2x1 (4628)
818900	2009-10-10 04:41:00	Rutherford good Nelson lad like me.	prefect (6291)
818901	2009-10-10 05:19:00	Loved it Ken. But is it true or apocryphal? :rolleyes: I don't know, but I hope it is true. Just to see that a couple of the greatest brains of the 20th century had a sense of humour!! Rutherford was at Havelock school as a child, and I believe he carved his initials in a desk while there - just like any other kid would do. My Great Grandfather was at that school around the same time I am told. I don't think any of the greatness rubbed of on any of us descendants ;) Ken	kenj (9738)
818902	2009-10-10 05:50:00	The Rutherford involvement is probably just a local variation on this oft told story :) Niels Bohr was a student in Denmark and went to Copengagen University. He didn't go to Rutherfords laboratory until 1912 when he already held a doctorate, so he wouldn't have been answering a first year question in elementary physics to Rutherford :banana I don't know if the basis of the story has any truth, or whether it is urban legend.	Terry Porritt (14)
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