A "fun" little physics question.

[ExigeEvan]

Simple really.

You're given a barometre and are asked to measure the height of a building.

How many ways can you think of doing it?

[EDIT] You don't just have a barometre, but be reasonable. Say, high school lab equipment.

 

[Stevisiov]

oooh I like a challenge although this sounds like out of the box thinking rather than physics
Famine has the answer no doubt.

 

[ExigeEvan]

It's simply a matter of applying the laws of physics, and abit of creativety.

The story behind it is that this was asked in an examination, and the person sitting the paper came up with many viable options before eventually coming up with the desired answer the examiners were looking for. It's sort of an Urban Myth of physics.

[EDIT] Quick edit to post 1.

 

[Kent]

I'm not much of a good student so this is probably beyond my skills... However...

If a barometer measures atmospheric pressure, then it could be possible to chart the change of pressure based on altitude, then compare ground level pressure to the pressure level at the top of the building.
Cross refference the difference between the ground level and building top level with any existing charts for changes based on altitude and you'll have the answer.

Of course, you'll also have to account for any natural differences in the atmosphere (which could change from day to day). With that in mind, I'm not really sure how you could find the height of said building (although like I said, I'm not much of a student for this sort of thing... ).

 

[ExigeEvan]

That's such a text book answer, you square!

Lets get the ball rolling...

Lets drop the barometre from the top of the building and time how long it takes to hit the ground.
S = displacement U= initial velocity a = acceleration (9.81ms^-2) t = time.

S=ut+0.5at^2

We know u is zero, a is 9.81 and that t can be measured. Plug it all into the formula and you get the height.

There are more things you can add. For example the air resistance, but I haven't reached that part of my course yet

 

[Philly]

you could drop it off the top of the building and see how long it takes to hit the ground and then factor in acceleration and wind resistance to find total distance traveled which would be the hieght of the building.

EDIT: Beat to it.

 

[Stevisiov]

That's such a text book answer, you square!

Lets get the ball rolling...

Lets drop the barometre from the top of the building and time how long it takes to hit the ground.
S = displacement U= initial velocity a = acceleration (9.81ms^-2) t = time.

S=ut+0.5at^2

We know u is zero, a is 9.81 and that t can be measured. Plug it all into the formula and you get the height.

There are more things you can add. For example the air resistance, but I haven't reached that part of my course yet

We wern't given a stop watch, photo finish equipment, PLUS, as it accelerates its air resistance increases, unless you work out its drag co-efficient and also plug the new air resistance formula into the already existing UVATS formula then it is going to be incorrect.

It is what annoyed me through high school maths last year, (well advanced mathmatics I took my GCSE maths in year 10 and there was no mechanics in that), it always takes place in an impossible scenario, like a frictionless plane, or assuming g(gravity) as 10, assuming there is no air resistance when you travel 100m/s etc. it would make things much harder but still it annoys me.

 

[ExigeEvan]

We wern't given a stop watch, photo finish equipment, PLUS, as it accelerates its air resistance increases, unless you work out its drag co-efficient and also lug the new air resistance formula into the already existing UVATS formula then it is going to be incorrect.

I did refer to my first post in an edit that allowed some basic equipment

The fact is that the desired answer, using the barometre and air pressure, wouldn't be completely accurate either, but it would still have been accurate enough to the examiners.

 

[Boundary Layer]

Y'know... this forum should be kept for actual questions with at least some degree of seriousness to them, and not jokes that have been recycled around the internet for years. We already have a Comedy forum.

I heard this 'problem' and the six or seven associated answers several years ago.

 

[Stevisiov]

^I edited above as well

since you took physics to college, which is what I am going to do, do you find the above annoying, off topic but worth asking.

For the above, thanks for your really productive post.

 

[ExigeEvan]

Well I never disputed that it had done the rounds, but I don't see why this thread appears to be lockable when to my knowledge (Of nearly last 4 years of GTP) it hasn't been posted before, and yet the plane ona conveyor belt thread still lives.

[EDIT] Not quite 4 years...

 

[daan]

You measure the length of the barometer, then use the barometer to measure the building.

 

[Stevisiov]

You measure the length of the barometer, then use the barometer to measure the building.

Thats what I first thought of, but it sounded like a cheap answer

 

[DustDriver]

Go to the designer of the building and ask him the height in exchange for the barometer

 

[Kylehnat]

Lets drop the barometre from the top of the building and time how long it takes to hit the ground.

Now you've broken a perfectly good barometer, thus raising the lab fee for everyone else. Thanks a lot.

 

[Wolfe]

Secure the barometer in an upright position on the ground, and measure both its height and the length of its shadow. Then measure the length of the building's shadow.

Do a little trigonometry and presto, you have the building's height.

 

[Rykon Zero]

take the barometer, put it on the ground, measure the reading, lift it 5 feet off the ground, record the settings, go to the top, record the settings, and then calculate how far you could throw a goat. burn your readings, get a ruler, get bitten by a radioactive spider, and measure the height using the written records you got from the buildings designer.

 

[Kylehnat]

At night, throw the barometer through the window of the county's Office of Public Records, then steal the blueprints.

 

[Sakiale]

Drop the barometer and measure how long it takes

Trade the owner the barometer for the building plans.

Damn it. You guys are too smart.

 

[ExigeEvan]

Finally! Some good answers here 👍

Also, tie a piece(s) of string to the barometre and lower it from the roof of the building to the ground and measure the string.

Use the markings on the barometre as a protractor and move a set distance from the building and measure the angle to the top of the building. Then use trig'. (Abit more far fetched I admit.)

Go to the designer of the building and ask him the height in exchange for the barometer

Exactly what my physics lecturer said.

 

[Stevisiov]

Secure the barometer in an upright position on the ground, and measure both its height and the length of its shadow. Then measure the length of the building's shadow.

Do a little trigonometry and presto, you have the building's height.

Thats a clever little solution, you just need to make sure you are quick between your readings or the sun will move to much, and throw out your results, of course we are talking fractions, but if its a tall building it can make quite a difference

take the barometer, put it on the ground, measure the reading, lift it 5 feet off the ground, record the settings, go to the top, record the settings, and then calculate how far you could throw a goat. burn your readings, get a ruler, get bitten by a radioactive spider, and measure the height using the written records you got from the buildings designer.

No idea what your on about be quite and don't post if that is all you have to say.

At night, throw the barometer through the window of the county's Office of Public Records, then steal the blueprints.

Thats also a very good idea, may find you in a small bit of trouble in the long run, but saves you brain a little working out.

Finally! Some good answers here 👍

Also, tie a piece(s) of string to the barometre and lower it from the roof of the building to the ground and measure the string.

Use the markings on the barometre as a protractor and move a set distance from the building and measure the angle to the top of the building. Then use trig'. (Abit more far fetched I admit.)


Exactly what my physics lecturer said.

Nice to see what I am getting myself into this year, in my college physics lessons.

 

[ExigeEvan]

Nice to see what I am getting myself into this year, in my college physics lessons.

This is all based on the 'easy' mechanics stuff, it's if/when you start doing quantum and quarks it gets difficult!

 

[Kylehnat]

Nice to see what I am getting myself into this year, in my college physics lessons.

And you will be answering pointless questions like this, and the airplane/conveyor question that's in another thread. The only difference is that your teachers will want "real" answers.

This is all based on the 'easy' mechanics stuff, it's if/when you start doing quantum and quarks it gets difficult!

Quantum mechanics is far more interesting than throwing a ball off a moving train and figuring out where it lands

 

[Stevisiov]

This is all based on the 'easy' mechanics stuff, it's if/when you start doing quantum and quarks it gets difficult!

Quarks as in sub-atomic particles? I have heard of them but not much else. I quite like the thought Quantum mechanics but have little understanding currently. I take it quantum mechanics is about space-time and relativity and stuff, or am I getting confused, after all we didn't do any in high school. But if so, I get the general idea, I just don't know the in depth science.

So yeah, be surprised as you may, I am actually quite excited about learning the stuff. My guess is that will all change when I have to do coursework on it.

[edit] I just check quantum mechanics on wiki, and it looks like I have it all wrong, I therefore am no longer looking forward to it.

 

[ExigeEvan]

And you will be answering pointless questions like this, and the airplane/conveyor question that's in another thread. The only difference is that your teachers will want "real" answers.

Not really. This question was merely asked by my lecturer when 6 people turned up for a lecture near the end of term. Yes, I was one of those 6.

Quantum mechanics is far more interesting than throwing a ball off a moving train and figuring out where it lands

Not to me. I'd much rather be able to throw a ball at the head of someone I dislike from a moving object than learn about things that while (strongly) proven are taught in an almost theoretical way. But it's different for everyone.

 

[Jimmy Enslashay]

Also, tie a piece(s) of string to the barometre and lower it from the roof of the building to the ground and measure the string.

But how long's a piece of string?

As for my answer? Look it up on Google.

Or Wikipedia.