The barometer problem

I found this story on another blog:


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 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.


It’s just a story but I think it’s quite nice :-). It exists in many different variants, and snopes.com has dated the first known version of it to 1958.

Spring, Opera and sneezing

It’s now really nice and warm outside. Unfortunately I sat mostly inside at the computer this weekend doing some programming and other stuff. However I did take a walk down to the new Opera building here in Oslo and took some images. It looks very nice. Not very cheap however, I read in the newspaper that around 4 billion NOK of tax money was used to build it. The same newspaper also mentioned that 8000 people from 700 different companies were involved in the building process. On saturday when I was there it was very crowded, you even had to stand in line on the small bridge over the road as it was so crowded in the staircase.

At the computer I tried to find a good way of drawing uml class diagrams in svg on linux. After testing different alternatives such as gaphor and umbrello I ended up using the old classic Dia. Gaphor was terribly buggy. Umbrello is ok, but it could not export proper SVG so I gave up on that too. Maybe there are nicer tools for this that I have not found ? Dia at least exported usable SVG after some tweaking of the fonts used.

Outside in the sun I immediately sneezed because of the bright light. I have sometimes wondered about this strange reflex but never cared to look it up. But now I did (on the net) and apparently it’s a genetic thing. However scientists do not know exactly why this happen for some people, except that the connections in the brain are a bit crosswired between the reflex that should close the iris and the sneeze reflex. I am not very bothered by it though. Also sneezing seem to be something that is not really needed in it’s current form in humans at all. Because it is thought that sneezing is supposed to clean out the nose to expell bacteria, pollen, virus and dirt. However humans sneeze almost completely with the mouth instead of the nose in contrast to other mammals. Check your dog or cat next time they sneeze, apparently they sneeze only with the nose (which is the proper and useful way of sneezing). So apparently it is a bit pointless to sneeze at all, and to sneeze when looking at the sun is then even more pointless :-). According to the report I found on the net around 20% of the Swedish population have this sun-sneeze reflex, I found that surprisingly high as I can’t recall having met someone else that have mentioned beeing affected by this, but then again I have never asked. And to be precise it’s not the sun in itself that causes it, for example if I have went to bed and been lying in the dark for some time and then decide to go up and turn on the computer; the bright light from the monitor is usually so bright that I have to sneeze :-).

Brainblast graphics

Improving the graphics does quite a lot to a game. I worked a while using Gimp and made a background which turned out quite nice. I found the tiles in a free tile set at lostgarden.com. There is still room for improvement of course, but it’s also a limit for how much time I can spend on this 🙂 And now the twoplayer mode has been removed (even though I hope to make that a choice later).

Brainblast progress

So I spent some more time on the little game that I have mentioned earlier. It’s now starting to actually closing in on becoming playable although there are still some parts missing for that such as a scoring system and level advancement. And the game is still set up as a twoplayer game although there is only one player playing, I obviously need to fix that 🙂

Anyway I updated the graphics such that it looks more like a game, but of course it needs to be improved more later. But at least the player is now a small doctor/wizard instead of a pepper 🙂 (By the way I have earlier called the pepper a paprice, where did I get that word from ?) Anyway now you can also put the falling pieces into place and not just look at them bouncing around.

Here is an image of how it looks now:

There are more and earlier screenshots here.