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.
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.
ATMOSPHERIC PRESSURE 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 clock‐driven revolving drum. Atmospheric pressure is expressed in several different systems of units: millimetres (or inches) of mercury, pounds per square inch (psi), dynes per square centimetre, millibars (mb), standard atmospheres, or kilopascals. Standard sea‐level pressure, by definition, equals 760 mm (29.92 inches) of mercury, 14.70 pounds per square inch, 1,013.25 × 103 dynes per square centimetre, 1,013.25 millibars, one standard atmosphere, or 101.35 kilopascals. Variations about these values are quite small; for example, the highest and lowest sea‐level pressures ever recorded are 32.01 inches (in the middle of Siberia) and 25.90 inches (in a typhoon in the South Pacific). The small variations in pressure that do exist largely determine the wind and storm patterns of the Earth. Near the Earth’s surface the pressure decreases with height at a rate of about 3.5 millibars for every 30 metres (100 feet). However, over cold air the decrease in pressure can be much steeper because its density is greater than warmer air. The pressure at 270,000 metres (10−6 mb) is comparable to that in the best man‐made vacuum ever attained. At heights above 1,500 to 3,000 metres (5,000 to 10,000 feet), the pressure is low enough to produce mountain sickness and severe physiological problems unless careful acclimatization is undertaken. Standard atmospheric pressure The standard atmosphere (symbol: atm) is a unit of pressure and is defined as being equal to 101.325 kPa. The following units are equivalent, but only to the number of decimal places displayed: 760 mmHg (torr), 29.92 inHg, 14.696 psi, 1013.25 millibars/hectopascal. One standard is standard pressure used for pneumatic fluid power (ISO R554), and in the aerospace (ISO 2533) and petroleum (ISO 5024) industries. In 1971, the International Union of Pure and Applied Chemistry (IUPAC) said that for the purposes of specifying the properties of substances, "the standard pressure" should be defined as precisely 100 kPa (≈750.01 torr) or 29.53 inHg rather than the 101.325 kPa value of “one standard atmosphere”. This value is used as the standard pressure for the compressor and the pneumatic tool industries (ISO 2787).
(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). 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
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. However, in Canadas public wea H n ather report sea leve pressure is ts, el instea reported in kilopas ad d scals , w while Environment Canadas stan ndard unit of pressu ure is the same  .) 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 Earths 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
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 PaL tem mperature la apse rate 0.0065 K K/mT0 sea level stand dard tempera ature 288.1 15 Kg Ea arth‐surface g gravitational l acceleration n 9.80665 m 2 m/sM mo olar mass of dry air 0.0289644 kg/m molR 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
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. 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.
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 theyll 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. Heres 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.
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. Its 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 its 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. 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 its 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.
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.
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