Atmospheric pressure is caused by the weight of air above the earth's surface. It can be measured using devices like barometers and manometers. The cabin of a pressurized aircraft is not maintained at 1 atmosphere (1 bar) of pressure because maintaining higher pressure inside allows passengers to breathe comfortably at high altitudes where air pressure is low. Exposure to large pressure changes rapidly can cause a medical condition called "bends" due to formation of gas bubbles in the body.

1. PRESSURE, WIND AND AIR
Discuss about Pressure, wind and air……………TABLE OF CONTENTS3. 1.0 INTRODUCTION3.
2.0 TYPES OF PRESSURE MEASURING DEVICES7. 3.0 REASON WHY A CABIN8. 4.0 BENDS9.
5.0 WIND10. 6.0 CONCLUSION11. 7.0 REFERENCE 1.0 IntroductionAtmospheric 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.TorricelliTorricelli 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 devicesBarometerA 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 WORKSThe 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

2. 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 gaugeA 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 continouslyThe 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)ManometerA 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 pressureAbsolute
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 pressureGauge 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
pressureDifferential 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

3. 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 BaThe 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
deepnessAtmosphere 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 BendsBends 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 WindWind 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). AirAir 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 AirAir 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
measurementAir measurement is important and necessary in that the humidity of air
affects many processes and technologies in industries, it also affects the health of
menThe Beaufort scaleThis 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

4. (Huller, & Scott, 2004).Instruments used for measuring wind speedAnemometerIt 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
SOCKSwind 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 airAir 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 pollutionThere 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 planesThe 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
ConclusionAtmospheric pressure measurement in necessary for weather forecasting as well
as wind measurement so as to avoid aircraft accidents. 7.0 ReferencesBoyes. 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– 1284West,J.B. (2002) Highest Permanent
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