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# Air pressure

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### Air pressure

1. 1. Atmospheric Pressure Mr. Gumjohn Yangyuen
2. 2. Air Pressure• Air pressure is the force exerted on you by the weight of tiny particles of air.• Though, the particles are invisible, they still have weight.• We are under high pressure but we do not realized because we are so used to it.
3. 3. Air Pressure• Atmospheric pressure is the force per unit area. (P = F/A)• Pressure decreases as altitude increases.• Atmospheric pressure is measured by a “barometer”.
4. 4. How heavy is air?• At sea level, the atmosphere exerts pressure on the Earth at a force of 14.7 pounds per square inch.• This means a column of air 1- inch square, extending from the surface up to the upper atmospheric limit, weighs about 14.7 pounds. 1 atm = 14.7 lb/in2 = 29.92 in Hg = 760 mm Hg = 105 N/m2 = 104 kg/m2 = 1013.2 mb (1 bar = 100 /m2)
5. 5. Measurement of atmospheric pressureThe barometer measures the height of acolumn of mercury inside a glass tube.A section of the mercury is exposed tothe pressure of the atmosphere, whichexerts a force on the mercury.An increase in pressure forces themercury to rise inside the tube; aspressure drops, mercury drains out ofthe tube, decreasing the height of thecolumn.This type of barometer is typically usedin a lab or weather observation station,is not easily transported, and is a bitdifficult to read.
6. 6. Aneroid BarometerThe aneroid barometer contains a closedvessel, that contracts or expands withchanges in pressure.The aneroid cell attaches to a pressureindicator with a mechanical linkage toprovide pressure readings.It is important to note that due to thelinkage mechanism of an aneroid barometer,it is not as accurate as a mercurialbarometer.Standard sea level pressure is defined as29.92 in. Hg. at 59°F (15°C) or 1013.2 Typical millibar pressure readings rangemillibars. from 950.0 to 1040.0 millibars.
7. 7. Effect of altitude on atmospheric pressure As altitude increases, pressure diminishes, as the weight of the air column decreases. On average, with every 1,000 feet of altitude increase, the atmospheric pressure decreases 1 inch of mercury. (every altitude +11m , pressure -1 mm Hg)
8. 8. • When altitude increases, pressure decreases, and water may boil at a temperature below 100°C • On every 27 mm Hg of atmospheric pressure increase, the B.P will decrease by 1°C
9. 9. Pressure VS Altitude P = 760 – (H/11) H = 11(760-P)Pressure VS Boiling Point B.P. = 100 – (760-P)/27 B.P. = 100 – (H/297)
10. 10. Pressure Cooker
11. 11. Why Do My Ears Pop?If youve ever traveled on a plane,or taken a lift up or down askyscraper, you might haveexperienced a weird or painfulsensation in your ears. This feelingis known as the popping of theears.But why do our ears pop?
12. 12. drum remains the same as it was at groundlevel. So, as you go up, the pressure insideyour ear drum becomes higher than the airpressure outside. Your ears then try to reducethe pressure inside. By doing so, the air insidepresses against your ear drums, making youfeel as if your ear drums are going to burst.On the other hand, if you descend rapidly, suchas when an airplane is touching down, thepressure of air outside the ear will be higherthan that of the air inside. The opposite willhappen. The air outside will press against yourear drums and you may feel pain.There is a tube inside our ears that helps tomaintain the pressure inside and outside ourear. It is called the Eustachian tube. This tubelinks the middle ear to the throat. A valve atthe end of the tube admits or releases air toequalise the pressure on the inside and
13. 13. Calculation Altitude-Pressure- and Boiling Point1) Find the altitude where the atmospheric pressure (429 m.) is 721 mm of Hg2) Find the atmospheric pressure on top of a (390 mm. Hg) mountain with 4,070 m. high. (92 °C)3) Find the boiling point of water on top of a mountain with 2,376 m. high. (95°C)4) Find the boiling point of water at a point where the atmospheric B.P-, H+ B.P-) is 625 mm of Hg (H- P-, P- pressure5) Explain the relation between A-P, P-B.P. and A-B.P.