Ch 02a Physics - Matter & Energy PDF

PHYSICS INTRODUCTION As an aviatio n maintenance techni c ian , you mus t ha ve a basic know ledge of p hysics, and the la w s that govern the behav ior o f th e materia ls wi th w hi c h yo u work. Ph ys ics is th e scie nce tha t d ea ls w ith matter and e nergy and their interac ti ons. Phys ics...

PHYSICS INTRODUCTION As an aviatio n maintenance techni c ian , you mus t ha ve a basic know ledge of p hysics, and the la w s that govern the behav ior o f th e materia ls wi th w hi c h yo u work. Ph ys ics is th e scie nce tha t d ea ls w ith matter and e nergy and their interac ti ons. Phys ics o pe ra tes wi th a bsolutes w hose properti es and va lues behove in th e same way every tim e. No t on ly d o these absol u tes make fligh t poss ible, hu t th ey a lso a ll ow e ng in eers a nti techni cians to d esign , bu ild , and m ainta in a ircra ft. MATTER AND ENERGY By defi n it io n , matter is a n yth ing tha t occup ies space a nd has ma ss. T he refore, the a ir. water. and food you need to live, as well a s the ai rc raft you mai n tain , arc a ll fo rm s o f malle r. T he Lmv of Co nse rvation s ta tes that matt e r cannot be crea ted or destroyed. You ca n , however, c hange the chara cter­ is t ics o f matter. Wh e n mat te r c hanges s tate, e n e rgy , wh ic h is the ab ility of maller lo do wo rk, can be ex tracted. Fo r example, as coa l is hea ted it c hanges from a so lid lo a combu s tibl e ga s w hi c h prod uces heat e nergy. OXYGEN 8 ELECTRONS 8 PROTONS 8 NEUTRONS CHEMICAL NATURE OF MATTER Fo r a be tter u ndersta nd ing of the ch a rac teris tics of m a tter, c hemis ts ty p ically red uce it to its bas ic uni ts. T he ato m is the bas ic u ni t of maller. The three sub­ ato m ic pa rti c les tha t form ato ms arc protons, neu­ tron s, and e lectrons. T he pos it ivc ly c harged pro to ns a nd th e n e utrons, w hic h have no e lectri cal cha rge, coex is t in a n a tom's n uc leus. The nega tive ly clwrged e lec tro ns orbit around the nu cleus in orderly rings, o r s hell s. The hydroge n a to m is th e si mpl est a tom. It has o ne pro ton in the n uc le us, no ne u Lro ns, and o ne e lect ron. The oxygen a to m is more com p lex. A n oxy­ gen atom con ta in s e ight protons a nd e ig ht neutrons in the nucl e us, a nd has e ight e le c tro ns o rb it ing aro und the nucle us. !rigure 2-1 1 HYDROGEN 1 ELECTRON 1 PROTON Figure 2-1. Th e hydro g e n atom h as on e p r oton , no n e u ­ tron s, and o ne e le ctr o n. Th e o xyg e n atom , on t h e othe r h a nd, h as e ight p r oto n s, e i g ht n e utrons, an d eig ht el ec­ t r o n s. ll owever. there is room for eigh t e lectro ns. There fo re, o ne oxyge n a tom ca n co m bin e w it h two hydrogen atoms by sha ring tho sing le e lectron from each hy drogen a tom. I Figure 2-3] PHYSICAL NATURE OF MATTER T he re are over 100 know n ele me nts. o r atoms. Each has an ide nt ifiab le nu mber of p rotons, neu trons, an d e lec trons. In additi o n , every ato m has it s ovvn ato mic number , as well as its ow n atomic ma ss. !Figure 2-2] Genera lly, w he n atoms bond togethe r th ey for m a molec ul e. Howeve r, th e re a re a few m o lec u les th a t exist as sing le atoms. 1\.vo exa mp les that yo u wi ll mos t like ly use in a ircra ft maintenance are he li um and argon. A ll other mo lecul es a re made up o f two or mo re ato ms. For examp le, water (H 2 0) is m a d e up oft wo a to ms o f hydrogen and o ne a tom o f oxygen. When atoms bond togethe r to fo rm a m o lecul e they s hare elec tro ns. fn th e examp le of H 2 0. the oxygen atom has s ix e lectro n s in its o ut e r, o r val e nce s he ll. Malte r is co mposed of severa l mo lecu les. T h e m ol­ ecu le is t h e s ma ll es l unit of a substa n ce (at leas t two atoms) th nl exh ibi ts th e ph ys ical and c h em i­ ca l pro pe rti es o f the substa nce. Fu rthe r more. all mo lecu les of a part icu la r s ubstance arc exactly a like a nd uniqu e Lo th at s ubs ta n ce. Ma tter ex is ts in d i ffe rent ph ys ica l slates. So lid. liquid , a nd g a seou s a re the three most co mmon ly e nco untered sta les a n d ar e di scussed in t h is text. A p h ys ical sta le refers to th e phys ica l cond itio n or a co mpo und , not lo a co mpo u nd 's c he m ica l s tr uc­ ture. In o t h e r \ v o rd s, ice, wa te r, and steam a re a ll 11 2 0, an d th e sa me ty p e of maller ap pears in a ll of th ese s tates. Physics 2-3......,... ~ Cit=Atomlc Number H 1.008 3 4 Li 6.941 Be 9.012 11 He Atomic Mass 4.003 6 8 B 10.81 c 7 12.01 N 14.01 0 12 13 14 15 Na ~~ 22.99 20 19 21 K Ca Sc 39.10 40.08 44.96 AI 26.98 Si 28.09 30.97 32.07 31 32 33 34 35 36 Ni Cu Zn Ga Ge Se As 78.96 58.69 63.55 69.72 72.61 74.92 65.39 Br 79.90 Kr 83.80 53 54 37 38 39 Rb 85.47 Sr 87.62 y 88.91 55 56 57 Cs Ba La 132.9 137.3 138.9 87 Fr 223 88 89 Ra Ac 227 226 5 Transition Elements 22 23 v Ti 47.88 50.94 40 41 24 25 27 26 Cr Mn Fe Co 52.00 55.85 54.94 58.93 42 43 45 44 28 46 29 47 30 48 Nb Mo Tc Ru Ag Cd Zr 92.91 Rh Pd 91.22 101.1 106.4 112.4 95.94 98.91 102.9 107.9 72 73 Hf Ta 178.5 180.9 104 105 74 75 76 w Os Re 166.2 190.2 106 107 183.9 77 lr 192.2 108 Rf Db Hs 267 ~~ Bh 272 277 268 y 109 78 79 80 Pt Au Hg 195.1 197.0 200.6 110 111 112 49 50 p 51 16.00 16 s 52 In Sn Sb Te 114.8 118.7 121.8 127.6 81 82 Tl 207.2 Pb 204.4 113 114 83 84 Bi Po 209.0 209 115 116 Rg Uub Uut Uuq Uuh Mt Ds Uup 291 281 289 276 280 285 284 288 9 10 Ne F 20.18 19.00 17 18 Cl 39.95 Ar 35.45 Xe I 131.3 126.9 85 86 At 210 Rn 222 117 118 (iJ)LW® Uuo 294 70 71 Lanthanides 58 59 60 61 62 63 64 65 66 Pm Sm Eu Gd Pr Nd Tb Dy ~0~ 140.9 144.2 144.9 150.4 152.0 157.2 158.9 162.5 67 Ho 164.9 68 69 Vb 175.0 Er Tm Lu 167.3 168.9 173.0 Actinides 90 91 Th 232 Pa 231 92 94 93 95 96 97 98 99 100 u ~~ Pu Am Cm Bk Cf Es Fm 238 242 243 247 247 251 252 257 101 102 103 Md No 259 Lr 262 258 Figure 2-2. This chart contains each of the known elements and their corresponding atomic numbers and atomic masses. All atoms and molecules in matter are constantly in motion. This motion is caused by the heat energy in the material. The degree of motion determines the physical state of matter. and, therefore, the molecules or atoms cannot move very far from their relative position. For this reason a solid is incompressible. LIQUID SOLID A solid has a definite volume and shape, and is independent of its container. For example, a rock that is put into a jar does not reshape itself to form to the jar. In a solid there is very little heat energy When heat energy is added to solid matter, the molecular movement increases. This causes the molecules to overcome their rigid shape. When a material changes from a solid to a liquid, the material's volume does not significantly change. However, the material conforms to the shape of the container its held in. An example of this is a melting ice cube. Liquids are also considered incompressible. Although the molecules of a liquid are farther apart than those of a solid, they are still not far enough apart to make compressing possible. Figure 2-3. A molecule of water (H 20) is formed when two atoms of hydrogen join one atom of oxygen. In a liquid, the molecules still partially bond together. This bonding force is known as surface tension and prevents liquids from expanding and spreading out in all directions. Surface tension is evident when a container is slightly over filled. [Figure 2-4] Physics 2-4 mass on earth as when in space. However, an ast ro­ naut's weight is much less when in space th an it is on ea rth. Ano th er definition sometim es used for mass is Lhe m eas m ement of an object's res is tance to ch ange its s tate ofrest or mo tion. Thi s is seen by comparing the force required to m ove a jet as com­ pared to a s ing le engine a irp lane. Because Lhe jel has a greater res istan ce to c hange, i t has a g rea ter mass. Th e mass of an object may be fou nd by di viding the we ight of the object by the accelera­ tion of grav ity, w hich is 32.2 feel per second every second an object fall s. Mass= Figure 2-4. A liquid conforms to the shape of the container it is held in. However, the cohesive force of the molecules forms a surface tension that allows the liquid to extend slightly above the container. Weight ­ Acceleration clue to gravity Both mass and weight are measu red in pounds in the Engl ish system and in gram s o r kilogra ms in the metr ic system. However, another common unit of measure for mass is the s lug. A slug is a unil of mass that is equivalent to approximately 32.175 pou nels und er s tandard atmosp heric cond itions. DENSITY GAS As h eat energy is continuall y added to a material , the molecular mo vement increases furth er until Lhe liquid reaches a point where surface tension can n o longer hold the molecules down. At this point Lhe molecu les escape as gas or vapor. The amo unt of heat required to change a liquid to a gas varies with different liquids and the amount of pressure a liquid is under. For example, at a press ure that is lower than atmos pheric, water boils at a tempera ture less than 212°F. Therefore, the boi ling po in t of a liq uid is said to var y directly with pressure. Gases d iffer from solid s and liquids in the facl Lhat th ey have neither a definite shape nor volume. Chemica lly, the molecul es in a gas are exactly th e sam e as they were in th e ir so lid or liqu id state. However, because the mo lecules in a gas are spread out, gasses are compressible. WEIGHT AND MASS Contrary to popular belief, the weight and mass of a material are not the sam e. Weight is the force with w hich gravity attracts a mass. However, it's more important Lo note th at the force of gravity vari es wi th th e dis tance between a bod y and the center of the earth. In other words, the far ther away an obj ecl is from the cen ter of the ea rth , the less il weighs. The mass of an object is described as th e amo unt of matter in an object an d is cons lanl regardless of its location. For exa mpl e, an as trona ut has the same The density of a substance is its weight per unil vo l­ ume. The den s ity of solids and liq ui ds varies with tempera ture. Ho·w ever, th e density of a gas var ies w ith temperature and pressm e. To find the density of a s ubstance, divide the weight of th e s ubstance by its volume. Th is res u lts in a weight per unil vol um e..t D ens1 y = Weig ht Vo lume For examp le, th e liquid wh ich fills a certa in con­ ta iner weig hs 1,497.6 pounds. The container is 4 fee l long, 3 feet wide, and 2 feet deep. T herefore, its vo lume is 24 cubic fee t (4ft. x 3ft. x 2 fl.). Based on this, th e liquid 's density is 62.4 lbs./ft3.. f 1,49 7.6 62.4 pounds per cu b1c oat = f 24 t 3 Because the density of solids and liquids var y with temperature, a s tandard temperatu re of 4°C is used when meas uring the densi ty of each. Although tem­ perature changes do not change the weigh t of a su b­ stance, they do change the volume of a su bstance throug h thermal expansion or contraction. Th is changes a s ubstance's weight per unit volume. As menti oned earlier, when meas uring Lhe density of a gas, temperature and press ure musl be cons id­ ered. Standard conditions for the measurement of gas density is establish ed at ooc and a press ure of 29.92 inches of mercury which is tbe average pres­ s ure of th e atmosphere al sea level. Physics 2-5 SPECIFIC GRAVITY ll is o fte n necessary to compa re the d e ns ity o f one s ubs ta nce w ith th at of another. For this reason, a s ta n da rd is needed fro m w hi ch a ll othe r mate rials ca n be co m p ared. The sta nd a rd when compa ring the d e ns ities o f a ll liq ui d s and solid s is wate r a t 4°C. Th e s ta nd ard fo r gases is air. In ph ys ics th e word "sp ecific " re fers to a ra ti o. Th e re fore, s pecific gravity is calc u lated by co mpar­ ing the we igh t of a d e fi nite vo lume of su bs tance with th e we igh t of a n equal volume of wate r. The follo wing formu las a re used to find spec ifi c g ra vit y (s p. gr.) o f liquid s and so lid s :. _ We ight of a subs tan ce s p. g1. - We ight of equa l volume of wate r s p.g r. = An exa mp le of speci fic grav it y th a t ho lds in te res t for a n av iatio n maintena n ce lechni c inn, is th e e lec trol y te of a l ead-acid b a t te ry. W h en a bat tery is d isc ha rged , th e calibra ted fl oa t i mme rsed in th e Den s it y of a s u bs tan ce Density of water Th e sa me fo rmu las a re used to find th e d en s ity of gases by s u bstituting a ir fo r water. Specifi c gravity is not e x pressed in u nits , b ut as a pu re numb er. Fo r exa mp le, if a ce rta in hydraul ic liqu id has a s pecil"ic gra vi ty of 0.8 , 1 c ub ic foo t of th e liqu id w e ighs 0.8 times as mu c h as 1 cu bic foot o f wa ter. S pec i fi e gra v ity is ind e p endent of th e size of th e samp le und e r cons id e ra ti on a nd varies only w ith th e su b­ stance t he sa mpl e is made o f. [Figure 2-5 1 LIQUID 1150 DISCHARGED SOLID Gasoli ne 0.72 Ice 0.917 Jet fuel JP-4 0.785 Aluminum 2.7 Jet fuel JP-5 0.871 Titanium 4.4 Alcohol (ethyl) 0.789 Zinc 7.1 7.9 Kerosene 0.82 Iron Lubricating oil 0.89 Brass 8.4 Synthetic oil 0.928 Copper 8.9 Water 1.000 Lead 11.4 Sulfuric acid 1.84 Gold 19.3 Platinum 21.5 Mercury A d evice called a h yd ro me te r is used to m eas ure th e specifi c g rav ity of liquid s. Thi s dev ice has a t ubu la r­ sh a p ed glass floa t con tain ed in a la rge r glass lube. T h e fl oa t is weighted and has a verti ca ll y grad u a ted sca le. The scale is read at t he surface of t he liq u id in whi c h t he floal is imme rsed. t\ read ing of 1000 is s h ovvn w h en th e float is immersed in pure w ater. Wh e n fi ll ed with a liq u id hav ing a densit y grea ter tha n pu re water, the fl oat rises a n d ind ica tes a g rea ter sp ecific gravity. For liquid s o f lesse r den s it y, t he fl oat si nks b el ow 1000. IPigu re 2-61 13.6 GASES Hydrogen Helium Acetylene Nitrogen Air Oxyg en Carbon dioxide 0.0695 0.138 0.898 0.967 1.000 1.105 1.528 Figure 2-5. This t ab le includes the specific gravity of com­ mon substances. The standard for liquids and solids is w ater w h er eas t he st and ard for gases is air. Both have a specific gravity of 1. Figure 2-6. The specific gravity of a liquid is m easured w ith a hydrometer. 2-6 Physics elec trol y te indi cates a pprox ima tel y 11 5 0. Th e indi ca ti on o r a c harged batte ry is bc tvvcc n 1275 a nd 1 300. S ince sp ec ifi c grav ity is based o n t h e dens ity o f lhc e lec tro ly te, lc m pe ra turc is a co n ­ s ide ra ti o n. Th e re fo re, ba llc ry e lecl ro ly te is mea­ s ured nt 80 d eg rees fo'a hre nh cil. If e lec tro ly te is a t a di ffe re nt lc mperal u re, a co rrecli o n m us t b e a ppl ied. ENERGY Energy, in its p ractica l form , is th e capacity of a n object to pe rform wo rk. It is classified into two ra th e r broad ty pes, p o te nti al and kin e ti c. The a m o u n t o f p o tenlia l e ne rgy possessed by a n e leva ted we ig ht is com p uted us ing th e followi ng fo rmul a: Pote nti a l Ene rgy = We ig ht x He ight When a spring is compressed or stre tc h ed from its no rma l co nditi o n , it possesses po te ntia l energy w hi c h ma y be released w he n the spring is all owed to re turn lo its a l-resl cond ition. Che m ical ene rgy is s lorcd in a n a ircra f'l bat tery a nd is th e re to p rod uce mechani cal work w hen the starter sw itc h is pressed. Electri cal e ne rgy can a lso be stored in a ca pacitor to prod uce ligh t w h en a s trobe light tube is fired. POTENTIAL ENERGY Poten ti al e ne rgy is ene rgy s to red in a ma te ria l. Even th ough a n object is not d oing work, it is ca pable o f d oing work. Pot e ntial e ne rgy is di vid ed in lo three groups : (1) !hal due to posilion , (2) th a t du e to dis­ torti o n of a n c las tic bod y, a nd (3) tha t w hi c h pro­ du ces wo rk throug h c hem ical action. T he e ne rgy a body possesses by virtu e o f its position or configuralio n is pote nti a l e ne rgy. T h is e ne rgy is s tored in th e bod y w h ic h re tains it, unti l it is pote n­ ti all y a ble to re lease il. !Pigurc 2-7].... /'...:> l - "I ? - --, ' \ I I I I