To measure building height by means of a barometer — the uncommon physical task showing how it is important for the physicist to think out of usual categories. The barometer measures atmospheric pressure, and nevertheless there is a set of ways to use this device for determination of height.

## It is required to you

- — barometer;
- — knowledge of physics;
- — it is a little imagination and sense of humour.

## Instruction

1. It is known that atmospheric pressure depends on height above sea level. Therefore, having measured air pressure at foundation of the building, and then having risen by a roof and having repeated measurement, it is possible to bring rise height out of the received difference. On average at rise on twelve meters atmospheric pressure decreases by 1 millimeter of mercury, or that the same, 133 Pas. Thus, if the difference in indications at the bottom and on a roof made 260-270 Pas, then equal 24 meters can consider height of the building.

2. For this way not only the barometer, but also a stop watch is necessary. Having dumped a barometer from a building roof, a stop watch note time of its falling. According to the equation describing the accelerated movement, the way passed by a body in free fall is equal (g*t^2)/2 where g is acceleration of gravity (9.8 м/с^2), and t is falling time. Having calculated a distance which the barometer before falling on the earth flew by on this formula, you receive building height.

3. Tie a barometer to a long rope and gradually lower it from a building roof on the earth. As soon as the barometer concerns the earth, measurement is complete. It is necessary only to go down on the earth and any way to measure rope length.

4. If it is difficult to measure rope length, the barometer can use as the pendulum. Time of fluctuations of the ideal mathematical pendulum depends only on its length and acceleration of gravity: T = 2π * √ (L/g) where T is the period of fluctuations, L — the pendulum length, and g — acceleration of gravity. Having measured the period of fluctuations of the barometer tied to a rope which length is equal to building height you will be able to calculate height on a formula: L = g * (T/2π)^2.

5. The shadows cast by objects are proportional to height of these objects. Therefore, having measured height of a barometer and length of a shadow which it casts on sunny day on a horizontal surface in a certain time of day, you will be able to divide them at each other, having received a proportion. Having measured length of the shadow cast by the building at the same time day and having increased it by the calculated proportion, you determine building height.