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Atmospheric pressure
1. UNIVERSIDAD DE SAN CARLOS DE GUATEMALA
Facultad de Ingeniería
TECHNICAL ENGLISH
SECCIÓN “A”
Atmospheric Pressure
POR:
Jaime Alexander Aguirre Ramos 200818410 Civil
Floridalma Esperanza Quintana Quiñones 200815490 Civil
Rossio Alejandra Zometa Herrarte 201213588 Civil
Fernando Martínez 200815406 Civil
Byron Sipaque 200818990 Civil
Guatemala, April 11th.
2.
INTRODUCTION
Atmospheric pressure, also called barometric pressure, force per unit area exerted by an
atmospheric column (that is, the entire body of air above the specified area).
Atmospheric pressure can be measured with a mercury barometer (hence the commonly
used synonym barometric pressure), which indicates the height of a column of mercury
that exactly balances the weight of the column of atmosphere over the barometer.
Atmospheric pressure is also measured using an aneroid barometer, in which the sensing
element is one or more hollow, partially evacuated, corrugated metal disks supported
against collapse by an inside or outside spring; the change in the shape of the disk with
changing pressure can be recorded using a pen arm and a clockdriven revolving drum.
OBJECTIVES
• Describe the atmospheric pressure and its effects on fluids.
• Demonstrate the Archimede’s Principle
• Understanding how atmospheric pressure affects.
4. (See also Standard temperature and pressure.) In
the United States, compressed air flow is often
measured in "standard cubic feet" per unit of time,
where the "standard" means the equivalent
quantity of air at standard temperature and
pressure. For every 1,000 feet you ascend, the
atmospheric pressure decreases by about 4%.
However, this standard atmosphere is defined
slightly differently: temperature = 20 °C (68 °F), air
density = 1.225 kg/m³ (0.0765 lb/cu ft), altitude =
sea level, and relative humidity = 20%. In the air
conditioner industry, the standard is often
temperature = 0 °C (32 °F) instead. For natural gas,
the Gas Processors Association (GPA) specifies a
standard temperature of 60 °F (15.6 °C), but allows 15 year average mean sea level pressure
a variety of "base" pressures, including 14.65 psi for June, July, and August (top) and
(101.0 kPa), 14.656 psi (101.05 kPa), 14.73 psi December, January, and February
(101.6 kPa) and 15.025 psi (103.59 kPa).[4] For a
(bottom)
given "base" pressure, the higher the air pressure,
the colder it is; the lower the air pressure, the warmer it is.
Mean sea level pressure (MSLP) is the pressure at sea level or (when measured at a
given elevation on land) the station pressure reduced to sea level assuming an
isothermal layer at the station temperature.
This is the pressure normally given in weather reports on radio, television, and
newspapers or on the Internet. When barometers in the home are set to match the
local weather reports, they measure pressure reduced to sea level, not the actual local
atmospheric pressure. See Altimeter (barometer vs. absolute).
The reduction to sea level means that the normal range of fluctuations in pressure is
the same for everyone. The pressures that are considered high pressure or low
pressure do not depend on geographical location. This makes isobars on a weather
map meaningful and useful tools.
The altimeter setting in aviation, set either QNH or QFE, is another atmospheric
pressure reduced to sea level, but the method of making this reduction differs slightly.
QNH
The barometric altimeter setting that will cause the altimeter to read airfield elevation
when on the airfield. In ISA temperature conditions the altimeter will read altitude
above mean sea level in the vicinity of the airfield
QFE
5. The barometric a altimeter se
etting that w
will cause an
n altimeter to read zero
o when at the
refere
ence datum of a particular airfie (in gen
m eld nway threshold). In IS
neral, a run SA
tempe erature conditions the altimeter w will read heiight above tthe datum iin the viciniity
of the
airfield.
QFE a QNH ar arbitrary Q codes r
and re y rather than abbreviatio
ons, but the mnemoni ics
"Nauttical Height"
" (for QNH) and "Field Elevation" (for QFE) arre often use ed by pilots to
distinguish them.
Avera age sealevel l pressure is
s 101.325 k kPa (1013.2 25 mbar, or hPa) or 29 9.92 inches of
mercu ury (inHg) o or 760 mill limeters (m mmHg). In aviation we eather repo orts (METAR R),
QNH is transmit tted around the world in milliba or hecto
d d ars opascals (1 millibar = 1
hectop pascal), exc cept in the U
United States, Canada, a and Colombia where it is reported in
inches s (to two de ecimal place es) of mercu ury. (The United States s and Canad da also repo ort
sea le
evel pressur SLP, whic is reduc to sea l
re ch ced level by a d
different mmethod, in the
remar section, not an inte
rks ernationally transmitte part of t code, in hectopasca
y ed the als
or miillibars.[5] However, in Canada's public wea
H n ather report sea leve pressure is
ts, el
instea reported in kilopas
ad d scals [1], w
while Environment Canada's stan ndard unit of
pressu ure is the same [2] [3].) In the we eather code e, three digi its are all th
hat is neede ed;
decimmal points an nd the one o or two most t significant
t digits are omitted: 10 013.2 mbar or
101.32 kPa is tra ansmitted a as 132; 1000 0.0 mbar or r 100.00 kP Pa is transm mitted as 00 00;
998.7 mbar or 99 9.87 kPa is transmitted d as 987; ettc. The high hest sealeve el pressure o on
Earth occurs in Siberia, wh here the Sib berian High often atta
h ains a seallevel pressu
ure
above e 1050.0 mb bar (105.00 kPa). The lo owest meas surable sea level pressu ure is found at
the ceenters of tro opical cyclonnes and torn nadoes.
Altitu
ude atmos
spheric pressure var
riation
Pressu varies smoothly f
ure from the Earth's surfa to the top of the mesospher
ace re.
Althou the pre
ugh essure channges with th weather, NASA has averaged th conditions
he he
for al parts of the earth y
ll year‐round. As altitud increases atmosphe
. de s, eric pressu
ure
decrea ases. One can calcu ulate the a atmospheri pressure at a giv
ic e ven altitud
de.
Temperature and d humidity a also affect t
the atmosph heric pressu
ure, and it is
s necessary to
know these to compute an accurate
6. Within the tropo
n osphere, th following equation relates atm
he g mospheric p
pressure p to
altitud
de h
where
e the consta
ant paramet
ters are as d
described be
elow:
ameter
Para iption
Descri Value
p0 sea level stand
dard atmosph
heric pressur
re 101325
5 Pa
L tem
mperature la
apse rate 0.0065 K
K/m
T0 sea level stand
dard tempera
ature 288.1
15 K
g Ea
arth‐surface g
gravitational
l acceleration
n 9.80665 m 2
m/s
M mo
olar mass of dry air 0.0289644 kg/m
mol
R un
niversal gas c
constant 8.31447 J/(mol
l•K)
Local
l atmospheric press
sure variat
tion
Atmosspheric preessure variies widely on Earth, and
these changes ar importan in studyin weather and
re nt ng r
climat See pre
te. essure syst
tem for the effects of air
e
pressu
ure variatioons on weathher.
Atmos spheric preessure showws a diurnal l or semidiuurnal
(twicee‐daily) cycle caused by global atm
mospheric t tides.
This effect is strongest in tropica zones, with
al
Hur
rricane Wilmaa on 19 Octob ber
amplitude of a feew millibarss, and almoost zero in p
polar
200
05–88.2 kPa (1
12.79 psi) in e
eye
areas.. These variiations have
e two superrimposed cy ycles,
a circ
cadian (24 h) cycle a
and semi‐ccircadian (112 h)
cycle.
Atmo
ospheric p
pressure re
ecords
The h
highest baro
ometric pre
essure ever recorded on Earth w 1,085.7 hectopasca
r was als
(32.06
6 inHg) mea asured in To
onsontseng gel, Mongolia on 19 Dec cember 20001.The lowe est
non‐toornadic atm
mospheric pressure eve er measuredd was 870 h hPa (25.69 in
nches), set o
on
7. 12 October 1979, during Typhoon Tip in the western Pacific Ocean. The measurement
was based on an instrumental observation made from a reconnaissance aircraft.
Atmospheric pressure based on height of water
Atmospheric pressure is often measured with a mercury barometer, and a height of
approximately 760 millimetres (30 in) of mercury is often used to illustrate (and
measure) atmospheric pressure. However, since mercury is not a substance that
humans commonly come in contact with, water often provides a more intuitive way to
visualize the pressure of one atmosphere.
One atmosphere (101 kPa or 14.7 psi) is the amount of pressure that can lift water
approximately 10.3 m (34 ft). Thus, a diver 10.3 m underwater experiences a pressure
of about 2 atmospheres (1 atm of air plus 1 atm of water). This is also the maximum
height to which a column of water can be drawn up by suction.
Low pressures such as natural gas lines are sometimes specified in inches of water,
typically written as w.c. (water column) or W.G. (inches water gauge). A typical gas
using residential appliance is rated for a maximum of 14 w.c., which is approximately
35 hPa.
In general, non‐professional barometers are aneroid barometers or strain gauge
based. See pressure measurement for a description of barometers.
Boiling point of water
Water boils at about 100 °C (212 °F) at standard
atmospheric pressure. The boiling point is the
temperature at which the vapor pressure is equal to
the atmospheric pressure around the water.
Because of this, the boiling point of water is lower at
lower pressure and higher at higher pressure. This
is why cooking at elevations more than 3,500 ft
(1,100 m) above sea level requires adjustments to
recipes.[10] A rough approximation of elevation can
be obtained by measuring the temperature at which
water boils; in the mid‐19th century, this method was used by explorers.
8. Experiments
SOLAR GLOBE
You can see that at:
http://www.youtube.com/watch?feature=player_embedded&v=zfEZTMbFZX4#!
Materials:
* Waste Bags Black
* Scissors
* Tape
* Hair Dryer
The larger the size of garbage bags that you get, the lighter will be your solar globe,
and you will avoid adding tape to join sections. But do not neglect the quality of the
bag. Being thinner, it will be lighter too, and is just what we need. So I do not
recommend the stock or good quality brand, as its high resistance is due to increased
film thickness.
The tape must be of medium or good quality, because if not paste properly, can ruin
your home to a hot air balloon flight time.
Procedure:
As you can imagine, this experiment is very simple. Just cut a lot of garbage bags with
the help of scissors. It is not easy to give an exact value of the dimensions, since they'll
depend of the final weight of your solar balloon, solar radiation in the area where you
live, etc.. But as a rule, the size of your balloon should be around one meter diameter,
and about four in length.
Thus, to calculate the dimensions of the piece you have to assemble, you have to
calculate the circumference of the globe. Here's an example:
We manufacture a solar balloon diameter of 1.5 meters and 5 meters long. The
perimeter of the same will be:
1.5 4.7
So the dimensions of the rectangle you have to create, hitting the bags of waste will be
4.7 meters x 5 meters.
To join sections, overlapping them or can put one right next to each other (I
recommend the latter). Forcibly presses the tape to the paste; recalled that the
adhesive tape classified using pressure sensitive adhesives.
9. Do not close your entire solar globe, leaving a small hole about 15 centimeters. They
put the hair dryer to inflate (careful not to burn the bag). When ready, close the hole
with tape. It's time for takeoff!
The following video is a clear and successful example of a home solar balloon in
operation.
How It Works
First of all, I would like a little clarification. The balloons solar powered solar
radiation, hot air hair dryer use it only to accelerate the process.
Everything has to do with the "famous" principle of Archimedes. While we have seen
in several experiments home, let us refresh her memory. He himself says that:
An object immersed in a fluid receives an upward force (called thrust), equal to the
weight of the displaced fluid volume.
Obviously the object is our balloon, and fluid is atmospheric air.
As our own solar balloon hot air, whose density is less than cold air, the weight of it
will be low. The force that pushes the balloon down, is the weight of it. On the other
hand, we push the atmospheric air exerts on the balloon. Would look like:
Weight
Thrust
When the weight of our balloon, is less than the thrust that it receives, when it is off
and is kept floating in the air. It seems strange to call this as "floating", but it's just
what happens, like a boat, but here the fluid is not water but a gas (atmospheric air).
When we add hot air hair dryer, the fluid within it begins to cool, since heat escapes it.
After several minutes, the density of air inside the balloon would be such that it could
not take off.
10.
But the sun does yours here as it stays warm the fluid. Not by chance, we indicated
that waste bags must be black. This makes our homemade balloon absorbs the most
solar radiation.
When the weight of our balloon, is less than the thrust that it receives, when it is off
and is kept floating in the air. It seems strange to call this as "floating", but it's just
what happens, like a boat, but here the fluid is not water but a gas (atmospheric air).
When we add hot air hair dryer, the fluid within it begins to cool, since heat escapes it.
After several minutes, the density of air inside the balloon would be such that it could
not take off.
But the sun does yours here as it stays warm the fluid. Not by chance, we indicated
that waste bags must be black. This makes our homemade balloon absorbs the most
solar radiation.
ATMOSPHERIC PRESSURE AND CANDIES
You can see that at:
http://www.youtube.com/watch?feature=player_embedded&v=WzdOxvDSfPA
To mention a couple, we can recall the experience called Experiment with air pressure
where we appreciate how easy it is crushed a can of soda, or the one published later
(Another experiment with atmospheric pressure) where an egg gets almost magically
in a container whose peak is smaller than him.
Today is the turn of the candy, which transforms this experiment in tempting and fun.
Materials:
* Container with vacuum pump
* Sweets
These containers are used in cooking, food storage vacuum.
Sweets are very common, although their name varies widely between different
countries. Can be found as "Baubles," "Gummy," etc.. They are made with sugar and
gelatin, which gives a very particular and rubbery.
11. Procedure:
This home is very simple experiment. Just put the candy in the bowl, cover and begin
to operate the vacuum pump. You see, the candy will begin to increase its size.
When you open the container, you will hear the sound of air entering the same and
watch the candy regain their size with great speed.
The following video shows step by step the experiment, and while it is in Spanish, you
do not understand anything of it, because what interests us is well illustrated.
How does it work?
As mentioned before, these kinds of candies are made with sugar and gelatin. What
gives you that look so rubbery, it is precisely the amount of air they contain. But the
air is perfectly enclosed and encapsulated in small bubbles, so you cannot escape from
there.
When we begin to operate the vacuum pump, the pressure inside the container starts
to decrease, but the pressure within the air bag remains sweets atmospheric pressure,
since, as mentioned, cannot escape.
So far, the pressure inside the bubbles of the candy is greater than the pressure within
the container, so that the first pushes out the walls of each airbag and sweet as the
material is less stiff, as its size increases magic.
When we opened the container, the pressure within it is equal to atmospheric, and
thus also the pressure inside the bubbles of sweet.
So that there is no more pressure exerting a force on the inner walls of the air bag.
Similarly, if we could increase the pressure inside the container, the opposite would
occur, and sweets decrease their size, and then would recover when opening the
container.
12. CONCLUSIONS
• Atmospheric pressure is the force per unit area exerted by an atmospheric.
• Atmospheric pressure can be measured with a mercury barometer.
• The Archimedes discovered the following principle an object is immersed in a
fluid is buoyed up by a force equal to the weight of the fluid displaced by the
object.
REFERENCE
Technical English Booklet. Universidad de San Carlos.
Engineering School. Second Edition
