Using a Barometer to Measure Height

Tie a long piece of string to the barometer, and lower it from the top of the building. Then pull it up and measure the string.

Jim

That doesn't demonstrate much knowledge of physics, you bozo!

Hank

I'd drop the barometer from the top of the building and time its fall. H = 1/2 GT².

Sally

DON'T YOU NITWITS KNOW ANYTHING??!! SWING THE BAROMETER FROM A SHORT STRING, MAKING A PENDULUM. TIME THE PERIOD AT THE BASE OF THE BUILDING, AND AGAIN AT THE TOP. T = 1/2 PI X SQ RT L/G. THE DIFFERENCE IN G GIVES YOU THE HEIGHT.

BUBBA

Bubba:

Turn off the darn caps! Furthermore, you answer is too complicated. Just lower the barometer from the top on a long string. Have a friend at ground level give it a push. time the period. no need to measure at both top and bottom.

Ernest

It is impossible to measure the height of a building with a barometer! Doing so would violate Newton's third law!

Isaac

ISAAC:

WHERE DID YOU BUY YOUR DEGREE? IT'S NEWTON'S SECOND LAW, NOT THE THIRD!

BUBBA

Bubba, you miserable moron:

I wasn't talking about Newton's second law (which I know, duh, has to do with friction or something). I was talking about Fig Newtons!

If the sun is shining, first measure the diameter of the barometer. Then stand it up vertically, and measure its shadow. Measure the shadow of the building. Figure the ratio.

Sunny

Maybe you could read the barometer at the base of the building, and then again at the top. 1" in HG equals 1000'. Easy?

Boyle

BOYLE:

THERE IS A DIFFERENCE BETWEEN "EASY" AND "LAZY." GET YOUR DICTIONARY OUT IF YOU DON'T KNOW THE DIFFERENCE! WITH THE TINY SCALE ON A BAROMETER, YOU'D BE LUCKY TO GET WITHIN 100' OF THE ACTUAL HEIGHT!!! THIS HAS GOT TO BE THE LAMEST ANSWER YET! WHAT WERE YOU THINKING???

BUBBA

This question reminds me of a time I was planning to go windsurfing. I was living near an inland lake at the time, and we rarely had good winds. The standard routine was to wait for an approaching thunderstorm, and then rush out and take advantage of the good winds, while attempting to avoid direct lightning strikes.

So to gauge the approach of the thunderstorm, I'd use a barometer, and rush to the lake after a half inch drop.

BTW. You may notice I spelled "gauge" "gauge" (instead of "gage"). I wonder if we, as a group, could standardize on one or the other. I'd like to hear what our friends from around the world have to say.

Am I getting off topic? I'm sorry, what was the question?

Too tempting:

http://www.oed.com/

Why do I get the feeling that our "guests" is just one person arguing with himself. All these "answers" come from an old story about Neils Bohrs, the Danish physicist.

Hi Vulcan

Hmmm... yes, it seems our guests could be one poster, doesn't it?

There is always some poster who posts in all caps, another who claims that (whatever) violates one of Newton's laws (even when it does not), another who's sarcastic, and yet another who, like me, can easily go off on a tangent.

When putting this together, I'd thought that others might add more out-of-the-box possibilities, having "primed the pump". How about selling the barometer so you can buy a tape measure?

Ken

If you have a watch and most people have it you do not need to measure the length since the pedulum period depends on the lenght. For a building height even a small one the period is big enough to obtain a good precision by measuring for instance 10 or 20 periods. Of course you will say that wind will complicate the problem or tha the presence of air will change the period nad introduce an error. But why buy a tape when you already have other simpler and lower cost possibilities. And why get rid of the barometer it can help later for weather predictions or may be I am wrong ?

Why are you sensitive to tangents?

Why are you sensitive to tangents?

Out of deep respect for trigonometry. I hate to see a tangent used when a sine really should be used.

Which reminds me of a story...

Where and which ?

Yes.

Hi ken,

Here's the whole story on Neils Bohr:

This concerns a question in a physics degree exam at the University of
Copenhagen: "Describe how to determine the height of a skyscraper with
a barometer."

One student replied: "You tie a long piece of string to the
neck of the barometer, then lower the barometer from the roof of the
skyscraper to the ground. The length of the string plus the length of
the barometer will equal the height of the building."

This highly original answer so incensed the examiner that the
student was failed immediately. He appealed on the grounds that his
answer was indisputably correct, and the university appointed an
independent arbiter to decide the case. The arbiter judged that the
answer was indeed correct, but did not display any noticeable knowledge
of physics. To resolve the problem it was decided to call the student
in and allow him six minutes in which to provide a verbal answer which
showed at least a minimal familiarity with the basic principles of
physics.

For five minutes the student sat in silence, forehead creased
in thought. The arbiter reminded him that time was running out, to
which the student replied that he had several extremely relevant
answers, but couldn't make up his mind which to use. On being advised
to hurry up the student replied as follows:

"Firstly, you could take the barometer up to the roof of the
skyscraper, drop it over the edge, and measure the time it takes to
reach the ground. The height of the building can then be worked out
from the formula H = 0.5g x t squared. But bad luck on the barometer.

"Or if the sun is shining you could measure the height of the
barometer, then set it on end and measure the length of its shadow.
Then you measure the length of the skyscraper's shadow, and thereafter
it is simple matter of proportional arithmetic to work out the height
of the skyscraper.

"But if you wanted to be highly scientific about it, you could
tie a short piece of string to the barometer and swing it like a
pendulum, first at ground level and then on the roof of the skyscraper.
The height is worked out by the difference in the gravitational
restoring force T = 2 pi sq root(l / g).

"Or if the skyscraper has an outside emergency staircase, it
would be easier to walk up it and mark off the height of the skyscraper
in barometer lengths, then add them up.

"If you merely wanted to be boring and orthodox about it, of
course, you could use the barometer to measure the air pressure on the
roof of the skyscraper and on the ground, and convert the difference in
millibars into feet to give the height of the building. But since we
are constantly being exhorted to exercise independence of mind and
apply scientific methods, undoubtedly the best way would be to knock on
the janitor's door and say to him 'If you would like a nice new
barometer, I will give you this one if you tell me the height of this
skyscraper'."

The student was Niels Bohr, the only Dane to win the Nobel
prize for Physics.

Read this and then the series of thread replies from "guest". It's all there. I'm pretty sure, all our guests (in this thread at least) is one and the same person.

Yes, there is no question that these "guests" were one person -- namely the guy sitting behind this computer!

It seems the story actually originated with Alexander Calandra: I've read the Niels Bohr story is a myth. Also Niels is not the only Dane to win the Nobel Prize. His son, Aage, and Ben Mottleson were also Danes and shared it (with James Rainwater) in 1975.

The original story: http://philosophy.lander.edu/intro/introbook2.1/x874.html

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

I'm aware that the story is supposed to be a myth. I was just amused that someone would use the inherent characteristic of a CR4 guest (anonymity) to stage an argument with himself.

I'm glad you were amused. The barometer story itself is amusing. But also I find the variety of responses on CR4 amusing, too. For example, we fairly often get people who proclaim loudly that certain phenomena are IMPOSSIBLE because they violate one of Newton's laws*. In fact, just before I posted all this, there was someone claiming that trust reverse CANNOT work on a jet boat because it violates conservation of momentum. In fact, thrust reversers (used an virtually all conventional jet boats -- but on very few PWC's ["jet skis"]) work just fine, and without them, a 30' jet boat would be an incredible handful to maneuver. (Of course, their operation does not violate any physics principal.)

Then there IS ALWAYS SOMEONE WHO POSTS IN ALL CAPS. And people, like me, who ramble on, often off-topic. It's all fun.

Ken

*We get an even greater number who claim that Newton's laws do not apply to their situation -- their perpetual motion machine will work just fine, they claim.

I would suggest to give the barometer to the house keeper and ask him for the building height. He knows it by heart. No need to go on top or to make complex time or length measurements. There is an other way which seems to me not so good but preaty correct: take a wire and let the barometer hang from top to ground and measure the length. There is a 3rd.valid if it is a quicksilver barometer: measure the length of the support, measure the length of your arm and look at the top of the building. A simple proportion will give the height. In fact it works as well with an aneroid barometer but with a lower accuracy.

... and even better with a water barometer!

Arguing with yourself is a symptom of schizophrenia (schizo: divided / Frenos: mind). Other symptoms are to hear voices, not recognizing a part of the body as belonging to it..or not recognizing yourself on the mirror. The latter does not apply to Dorian Grey nor to vampires!

Uhh...Ohhh.. If I can recognize myself in the mirror about half the time is that OK?

It probably means that one of your personalities is really sick!

Guest could have MPD (multiple personality disorder) then technically it is not the same person.

How accurate is the barometer method if you go up the elevator and the weather changes? then there would be an error in the measurement

How accurate is the barometer method if you go up the elevator and the weather changes? then there would be an error in the measurement

Simple. Check the weather report before you take your readings. They always give the barometric pressure, normalized to sea level, and indicate if it is rising, lowering or steady. If it is lowering, then stormy weather could be on the way. If it is rising or steady, then the weather will be fair. Chose a day with fair weather for your measurements. Also, double check with your GPS.