atmosphere - the gas cloud surrounding Earth.The weight of the air column height in excess of 900 km, has a powerful impact on the inhabitants of our planet.We do not feel this, seeing life on the bottom of the ocean air for granted.The discomfort the person feels, rising high in the mountains.Lack of oxygen triggers fatigue.Thus varies substantially atmospheric pressure.
Physics examines the atmospheric pressure and its changes and impact on the Earth's surface.
In the course of physics of high school study of the action of the atmosphere has received considerable attention.Features definitions, depending on the height, the impact on the processes occurring in the home or in nature are explained on the basis of knowledge about the effects of the atmosphere.
When beginning to study the atmospheric pressure?Grade 6 - time acquaintance with the peculiarities of the atmosphere.Continue this process in core high school classes.
history study
first attempt to establish the atmospheric pressure of the air taken in 1643 at the suggestion of the Italian Evangelista Torricelli.The glass sealed at one end of the tube was filled with mercury.Closing on the other hand, it was lowered into the mercury.At the top of the tube due to partial leakage of mercury formed an empty space, the following title: "Torricellian emptiness."
By this time in science dominated by the theory of Aristotle, who believed that "nature abhors a vacuum."According to his views, empty, space is not filled with a substance can not be.Therefore, the presence of voids in the glass tube long tried to explain other mothers.
The fact that it is an empty space, no doubt, it in no way can be filled, as the mercury to the beginning of the experiment completely filled cylinder.And emerging did not allow other substances to fill the vacant position.But why are not all of the mercury poured into the vessel, as well as the obstacles it not?The conclusion is clear: the mercury in the tube as in communicating vessels, creates the same pressure on the mercury in the vessel as something from the outside.On the same level with the surface of the mercury just touching atmosphere.It retains its pressure substance from flowing out by gravity.Gas, as is known, produces the same effect in all directions.His influence is exposed to the surface of the mercury in the vessel.
mercury height of the cylinder is approximately equal to 76 cm. It is noted that this figure varies over time, so that the pressure of the atmosphere is changing.It can be measured in cm Hg (or millimeters).
What unit to use?
International System of Units is international, so it does not involve the use of millimeters of mercury.Art.at a certain pressure.Unit atmospheric pressure is set the same way as it occurs in solids and liquids.Pressure measurement in Pascal accepted in SI.
For 1 Pa taken such pressure that is created by force H 1 attributable to the area of 1 m2.
determine how the linked units.The pressure of the liquid column is set by the following formula: p = ρgh.Ρ = density of mercury 13600 kg / m3.For a starting point we take the mercury length of 760 millimeters.From:
p = 13600 kg / m3 × 9,83 N / kg × 0,76 m = 101,292.8 Pa
To record the atmospheric pressure in Pascals, consider: 1 mmHg= 133.3 Pa.
Example solving
Determine the force with which the atmosphere acts on the surface of the roof the size of 10x20 m. The pressure of the atmosphere considered equal to 740 mm Hg
p = 740 mm Hg, a = 10 m, b = 20 m.
analysis to determine the potency necessary to establish the atmospheric pressure in Pascals.Considering that 1 mm Hgequal to 133.3 Pa, we have the following: p = 98 642 Pa.
decision
use the formula determining the pressure:
p = F / s,
Since the roof area is not given, we assume that it has the shape of a rectangle.The area of this figure by the formula:
s = ab.
substitute the value of the area to a calculation formula:
p = F / (ab), where:
F = pab.
We calculate: F = 98 642 Pa × 10 m × 20 m = 19728400 N = 1.97 MN.
Answer: The power of atmospheric pressure on the roof of the house equal to 1.97 MN.
Methods for measuring
Experimental determination of atmospheric pressure can be performed using a column of mercury.If next to it to fix the scale, it becomes possible to capture changes.This is the easiest mercury barometer.
noted with surprise changes in atmospheric action was Evangelista Torricelli, linking this process with the heat and cold.
optimum was named the atmospheric pressure at sea level at 0 degrees Celsius.This value is 760 mmHgAverage atmospheric pressure in Pascals is considered to be equal to 105 Pa.
known that mercury is quite harmful to human health.As a result, the open mercury barometers can be used.Other liquids have a density much less, so tube filled with liquid should be long enough.
For example, the water column generated Blaise Pascal, should be about 10 m in height.The disadvantage is obvious.
aneroid barometer
remarkable step forward can be called away from the idea to create a liquid barometers.The ability to produce a device for detecting the pressure of the atmosphere is implemented in the aneroid barometer.
main part of the meter - a flat box from which air is pumped out.That it is not squeezed atmosphere makes corrugated surface.Box spring system connected with an arrow indicating the pressure value on the scale.The latter can calibrate in any units.Measures the air pressure in pascals at possible corresponding measuring scale.
lifting height and atmospheric pressure
Changing the density of the atmosphere as they rise up reduces the pressure.The heterogeneity of the gas shell does not allow to enter the linear law changes as altitude increases the degree of pressure reduction is decreased.At the Earth's surface as they rise for every 12 meters of the action of the atmosphere falls 1 mm Hg.Art.In the troposphere, a similar change occurs in every 10.5 m.
Near the Earth's surface, in the altitude of the aircraft, aneroid fitted with a special scale can determine the height of the atmospheric pressure.This instrument is called an altimeter.
special device on the surface of the Earth allows you to set the altimeter to zero in order to continue to use it to determine the lift.
example of solving the problem
at the foot of the barometer showed atmospheric pressure 756 mm Hg inWhat is to be at the height of 2500 meters above sea level?You want to record atmospheric pressure in Pascals.
p1 = 756 mm Hg, H = 2500 m, p2 -?
decision
To determine the barometer at a height H, take into account that the pressure drops by 1 mm Hgevery 12 meters.Therefore:
(p1 - p2) × 12 m × N = 1 mm Hg, where:
p2 = p1 - N × 1 mm Hg / 12 m = 756 mmHg- 2500 m × 1 mm Hg / 12 m = 546 mmHg
To record the resulting atmospheric pressure in Pascals, follow these steps:
p2 = 546 × 133,3 Pa = 72,619 Pa
Answer: 72,619 Pa.
atmospheric pressure and weather
movement of air atmospheric layers near the surface of the Earth and the nonuniform heating of air in different areas lead to a change in weather conditions in all areas of the planet.
pressure can vary by 20-35 mmHgin the long run and 2-4 millimeters of mercuryduring the day.A healthy person does not perceive changes in this indicator.
atmospheric pressure which is lower than normal and often change indicates a cyclone, cover certain.Often this phenomenon is accompanied by clouds and precipitation.
low pressure is not always a sign of rainy weather.Bad weather is more dependent on the gradual decline of this indicator.
sharp drop in pressure up to 74 cm Hgand lower faces storm rains that continue even when the index is already beginning to rise.
weather changes for the better can be determined by the following features:
- after a long period of bad weather there is a gradual and steady growth of atmospheric pressure;
- in foggy slushy weather increases pressure;
- during southern winds this indicator rises for several days;
- increase in atmospheric pressure in windy weather - a sign of the establishment of comfortable weather.
