# PRESSURE, WIND AND AIR

Discuss about Pressure, wind and air

3. 1.0 INTRODUCTION
3
. 2.0 TYPES OF PRESSURE MEASURING DEVICES
7. 3.0 REASON WHY A CABIN
8. 4.0 BENDS
9. 5.0 WIND
10. 6.0 CONCLUSION
11. 7.0 REFERENCE

1.0  Introduction

Atmospheric Pressure can be a unit area of force it puts on the surface by the mass of air on top of that surface in this case the earths surface or any other planet for that matter. In most cases atmospheric pressure is assumed to be hydrostatic pressure which is pressure of a static medium.
Torricelli
Torricelli was born in the states of Papal in a place called Faenza; Torricelli was inspired by Galileos science inventions, his idea of trying to solve practical problems led him to invent the mercury barometer. This barometer consisted of mercury which was denser than water almost 14 times, one metre tube closed at the top, after filling it with mercury. He then set in a basin in a vertical manner; the mercury column fell to almost 76 cm, thus leaving a vacuum above, a vacuum that was later called as Torricellian vacuum. With changing atmospheric pressure the height of the column fluctuated.
2.0 Types of pressure measuring devices
Barometer
A barometer is an instrument that is commonly used to measures atmospheric pressure. Barometers are of two types :mercury barometers which are common and  aneroid barometers which are digital.The figure below show an example of a mercury barometer;

HOW THE BAROMETER WORKS
The barometer in  the figure above works in a way of balancing the mercury weight in the tube  of glass with the atmosphere pressure just like a couple of scales.The level of mercury in the glass tube will rise if the mercury weight is less that of the atmospheric pressure;and if the mercury weight is higher than that of atmospheric pressure ,the level of mercury will fall.Since the atmospheric  pressure is the weight of air on top of the reservoir ,therefore the mercury level keeps changing  until the mercury weight in the tube of glass balances equally with the weight air on top of the reservoir.
Measurements of atmospheric pressure changes help in weather forecasting this is because the  pattern of weather changes  are taken from  high and low pressure regions.Therefore through monitoring the barometric pressure levels,local weather forcasting can be done  using the following simplified guidelines;
1.If the pressure in the barometer decreases it shows that  it will be a rainy,windy and stormy weather.
2.If the pressure in the barometer increases it shows that it will be a dry,sunny and cold weather.
3.If pressure  falls in a regular,slow and moderate manner this indicates that pressure passing in the sorrounding regions is low thus its very unlikely to find marked weather changes.
4.If pressure decreases rapidly that  indicates that there is change in the weather in the nearby area .Wind spells and showers follow briefly.
5.If the pressure drops sharpely in a short time it shows the place will experience storms in a minimum of six hours.
6.If pressure decreases largely but slowly it shows poor weather will prevail in a long time ,a more pronounced weather will prevail if the pressure rose before it started dropping.
7.If pressure rises rapidly,during a weather codition that is fair and average,it shows that the cell pressure is low meaning that soon there will be a decrease in pressure hence a poor weather is expected.
8.If there is low pressure and then there happens to be a quick rise in pressure ,that indicates that a fair period of weather is expected.
9.If there is a large pressure rise, slowly and constantly ,a good weather  is expected for a longer period.
Vacuum gauge
A vacuum gauge is used in the measurements of pressure in a vacuum.The gauge is divided further into  two categories which are low and high vacuum.If several gauges of different kinds  are combined ,using different techniques they can possibly measure a pressure system continously

The face of the vacuum gauge are in inches graduation of mercury,a millimeter scale of mercury is  aIDed into it.It sholud be noted  that many of the vacuum gauges have have been fitted with another scale that measures pump  pressure of fuel.In using the vacuum gauge you always need to to connect it to a source of vacuum constantly from an engine. (Robert, 1990)

Manometer

A manometer is just a mercury filled U-shaped tube that is used to measure pressure.One end of the manometer is connected to a vessel which has unknown pressure while the other end is connected to the atmosphere.When the closing valve is opened ,the mercury will be pushed by the vessel if the pressure is higher compared to the atmosphere,on the other hand the vessel will pull the mercury if the prsessure is low as compared to the atmosphere.The mercury height column differences on both sides of the U shows you how much pressure is high or low in the container as compared to the atmosphere. (Boyes, 2008).
Absolute pressure
Absolute pressure can be defined as pressure got from the aIDition gage pressure plus the local pressure of the atmospheres value,i.e. it is the pressure measured in relation with a vacuum that is perfect.
Gauge pressure
Gauge pressure is the pressure got from subtracting atmospheric pressure from absolute pressure.The negative sign in the end result is always ignored.i.e.pressure measured relative to air pressure (ambient pressure)
Differrential pressure
Differential pressure is simply the pressure difference between  two given points,i.e two pressure sources.It is normally expressed in square inch per a given pound.Differential pressure is mainly used in the measurement of the difference of pressure of gas or fluid across a pipe that is restricted.Determination of the flow is then done by the conversion of the reading of differential pressure using bernoullis equation.Since the deifferential pressures square root is proportional to the flow in a closed vessel,then in most times its preffered to use the output signals square root  for simplification of the conversion to flow measurement. The measurement of differential pressure can be applied in; measurement of hydrostatic level of contents of a tank which has gas that is not vented at the top.Thus the pressure difference is measured between the top and the bottom to help in the determination of hydrostatic pressure that is true.
Secondly measurement of differential pressure helps in monitoring leakages between components that are test pressurised and reference pressure that is controlled .Airspeed which gives two air channels,used for maesuring air pressure total and static pressure using a pitot vessel.The air velocity pressure is got from the difference of the two channels.This technique is applied to measure the airspeed on aircrafts and tunnels of wind for simulation of air velocity so as to test an objects aerodynamics.
3.0 Reason why a cabin of a pressurized aircraft is not maintained at 1 Ba
The cabin of an aircraft which is pressurized is not maintained at 1 Ba this is because as it flies higher to the atmosphere the air pressure reduces thus this makes breathing hard and can cause more problems like decompression,which is a type of sickness that arises from gases that come out a solution and they are dissolved, while depressurisation is taking place in a body. The advantage of not maintaining the cabin that is pressurised of an aircraft at 1 Ba is it allows passengers including pilots to comfortably breathe at certain attitudes where the air is thin. Another advantage is that since the air desires to move out through the small cracks within the aircraft, it is then easier for the cabin to be heated because there is no flow of cold air. To a larger extent some aircraft increase their strength structurally using their cabin pressure.
The atmospheres deepness
Atmosphere can be defined as gases that form an envelope around the planet earth. The question on how deep the atmosphere is does not have a specific answer because there is no available device that can be used to measure the depth of the atmosphere exactly but it is believed to be 33ft below the surface of water, (West 2002)
Importance of measurement of pressure.
One major importance of measuring atmospheric pressure is that it helps in the prediction of weather patterns, thus helping in weather forecasting. In pipes its important to monitor pressure so as to avoid damage due to production of small droplets that are susceptible to the drift of the wind.
4.0 Bends
Bends can be defined as a type of sickness that develops to a person who has been exposed to a reduced pressure around the persons body. The main causes of bends are; a diver ascending from a dive rapidly stopping after a deep dive; an aircraft flying upwards which is unpressurised; an aircrafts cabin failure in its pressurization system; divers flying shortly in an aircraft; a worker coming out of a mine that has been pressurized to keep out water; an astronaut who is trying to exit the space vehicle and do a space walk where the pressure in the vehicle is higher than his spacesuit.
5.0 Wind
Wind can be categorized as gases that are flowing together on a large scale. The bulk of air movement on earth constitute wind. Winds are always classified according to their strength, and direction they are flowing from in meteorology. Short burst winds which are in high speed are called gusts while winds which are strong for a shorter duration are known as squalls. (JetStream2008).
Air
Air is defined as a combination of gases that are surrounding the plane earth. Different planets have different composition of air that surrounds them.
Composition of Air
Air is composed gases which are mainly oxygen, nitrogen and argon.Dry air has the following percentages in terms of composition nitrogen 78%, oxygen 21%, argon 0.9% and other small amounts of other gases like carbon dioxide. There is evidence that due to industrialization the composition of air has changed remarkably this is so because of the establishment of many factories which emit a number of  gases that mix with air and thus have weakened the layer of the atmosphere a condition that is now known as global warming.
Importance of air measurement
Air measurement is important and necessary in that the humidity of air affects many processes and technologies in industries, it also affects the health of men
The Beaufort scale
This scale relates to the measurement of wind speed empirically and the conditions observed on land and at sea. It was discovered in 1805 by Francis Beaufort (Huller, & Scott, 2004).
Instruments used for measuring wind speed
Anemometer
It is a device used for measuring the speed of the wind and it is common instrument in a typical weather station.

Its made up of four cups that are hemispherical in nature mounted on the ends of the four arms which are horizontal. The cups are at certain angles to each other on the shaft which is vertical. Therefore to determine the speed of wind, the numbers of turns the cups make over a given period of time give the average speed of the wind.
WIND SOCKS
wind socks are generally used to measure the speed of wind as well as show the direction of wind. They are normally found areas that are open like airports and seaports. They show direction by socks pointing towards where the wind is blowing. The wind strength is shown from the movement of the wind sock.
Pollution of air
Air pollution is when harmful biological materials, chemicals or matter that causes human discomfort and living organisms thus causing damage to the atmosphere. This air pollution can be measured directly at the source as its emitted or it can be measured as a concentration in the atmosphere, this is done by the help of computer simulated methods and models.
Effects of air pollution
There are many effects that are associated with air pollution like; global warming which is caused by gases such as methane, carbon dioxide and ozone that are generated by greenhouse; acid deposition which is done by the rain, this affects soil and water resources; salination of resources of water due to nitrates and sulphates accumulation.
American attacking planes
The American planes while attacking Tokyo in 1944, the planes moved backwards, this is because when the wind was approaching them they were moving at a slow speed thus it forced them to flow backwards.
6.0 Conclusion
Atmospheric pressure measurement in necessary for weather forecasting as well as wind measurement so as to avoid aircraft accidents.

7.0 References

Boyes. W. (2008). Instrumentation Reference Book, Fourth Edition. Butterworth-Heinemann. pp.1312.
Huler, S. (2004). Defining the Wind: The Beaufort scale, and How a 19th-Century Admiral Turned Science into Poetry. Crown.ISBN 1-4000-4884-2.
JetStream  (2008). Origin of WindNational Weather Service Southern Region Headquarters. Retrieved  2009-02-16.
Robert M. B., ed. (1990). Vacuum Techniques. The Encyclopedia of Physics (3rd ed.). Van Nostrand Reinhold, New York. pp. 12781284
West,J.B. (2002) Highest Permanent Human Habitation.Hiigh altitude medicine & Biology,3,401-407

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