General Question

How's avatar

How to find the height of a building?

Asked by How (4 points ) August 3rd, 2009

by what method, find out the way of finding height, what instrument is suitable for it..

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21 Answers

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se_ven's avatar

Google, search building name, internet capable computer ;)

ragingloli's avatar

climb on top, drop stone, measure time with a stop watch, calculate.

PerryDolia's avatar

You can use a little trigonometry.

Measure your distance from the building. This is the base of the triangle.

Use a simple straw and protractor to get the angle. Look through the straw to see the top of the building, measure the angle with the protractor.

Now you have the adjacent length and the angle.

Use the tangent (opp/adj) of the angle to calculate the height of the building.

Jayne's avatar

@ragingloli, only if you know the coefficient of air friction of the stone, and can assume ideal behavior, still air, etc :)

se_ven's avatar

Equation for @ragingloli‘s method:

x = ½ * a * t^2 Where x = height, a = acceleration of gravity, t = time

Link

dpworkin's avatar

@teh_kvlt_liberal has distilled it as far as one can. That made me smile. It also helps to know that height = base times tan(angle).

Also, remember your Pythagorus: Where c= the Hypotenuse, a= height and b= width, c = square root of (a squared + b squared)

Christian95's avatar

“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.”

A funny way to do it.

This answer was given by Nils Bohr( http://en.wikipedia.org/wiki/Niels_Bohr)

Jayne's avatar

@se_ven; no, because that assumes a constant force, whereas air resistance causes the force to be in rough inverse proportion to velocity. Also, if the building is very tall, the curvature of the earth comes into effect. Because the top of a building is further from the center of the earth than the base, it is moving faster with the rotation of the earth. Thus, a stone dropped with the same horizontal velocity as the top of the building will, when it reaches the bottom, be moving relative to the ground, and will land somewhat to the east of the building’s base. As the earth is curved, this also means that it will fall somewhat further than it otherwise would have; or at least, irregular terrain implies that the distance fallen is probably not the same as the height of the building. In fact, if the building is tall enough, it may go into orbit. This effect is lessened by air resistance, of course.

For those who can’t tell, I’m just having fun here. Just use trig as others have suggested.

zephyr826's avatar

You can also (if there’s nothing around the building and it’s sunny) use the shadows. Get a 3 foot stick (a yardtick perhaps…) and place it perpendicular to the ground – then measure its shadow. Meanwhile, have a friend measure the shadow of the building and set up a ratio.

3ft/(shadow of stick) = x (height of building)/(shadow of building)

(also, welcome to Fluther, @How )

Fred931's avatar

If you’re asking how designers do this when they have a building built… I sure hope that they think it through when they design it… :P

Christian95's avatar

This is my own simple way:
you walk from the base of the building(and measure the distance D)until a point where you see the top of the building at an angle of 45degrees(you can easily measure this using your arms).Results that the 3rd angle of the triangle formed by you,the top and the base of the building measures 45degrees too.This means that the triangle is isosceles.As a result you get that the distance D is equal with the height H of the building

se_ven's avatar

Oh @Jayne you’re getting too technical…

I like my physics like I like my dirt, in a vacuum! :)

LuckyGuy's avatar

A Garmin GPS will do it for you two ways:
1) Wait until you get a lock with at least 5 satellites while you are on the ground and read the height above sea level . Go to the roof and take another reading. Subtract the two.
2) Find the superintendent and say “I’ll give you this Garmin if you tell me the height of this building.

mea05key's avatar

@PerryDolia

I am bit slow overhere, what’s the use of the straw? I am assuming we are measuring a tall building (100m height and above).

dpworkin's avatar

you use the straw with a protractor to help determine angle of ascent.

mea05key's avatar

So I am looking at the 100m building and I am standing say 50m away from the building straw. I understand that the straw is used to help to determind the angle of the building with the protractor. But I see that it would be difficult to point the straw to the top tip of the building accurately. I have the feeling there will be a lot of visual errors when reading the value from the protractor.

dpworkin's avatar

Look through the straw.

Haffi112's avatar

Use a barometer! :D

ragingloli's avatar

Use witchcraft! :D

tramnineteen's avatar

Get string, tie a weight to the end and just lower it down till you see it hit bottom and measure the string in sections later in the comfort of your home with a beer!

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