Koj tuaj yeem xav txog dab tsi cov nthwv dej yog dab tsi los ntawm kev pov pob zeb rau hauv dej. Cov voj voog uas tshwm sim rau ntawm nws thiab hloov pauv troughs thiab ridges yog ib qho piv txwv ntawm cov tshuab tsis muaj zog. Lawv qhov essence yog dab tsi? Mechanical yoj yog cov txheej txheem ntawm kev co propagation nyob rau hauv elastic media.
Nyob rau ntawm cov kua dej
Cov khoom siv tsis zoo li no tshwm sim vim muaj kev cuam tshuam ntawm lub zog nruab nrab thiab lub ntiajteb txawj nqus ntawm cov khoom ntawm cov kua. Tib neeg tau kawm txog qhov tshwm sim no ntev. Qhov tseem ceeb tshaj plaws yog dej hiav txwv thiab dej hiav txwv. Raws li cua ceev nce, lawv hloov thiab lawv qhov siab nce. Cov duab ntawm cov nthwv dej lawv tus kheej kuj yuav nyuaj dua. Hauv dej hiav txwv, lawv tuaj yeem ncav cuag qhov txaus ntshai. Ib qho piv txwv meej tshaj plaws ntawm kev quab yuam yog tsunami uas cheb txhua yam hauv nws txoj kev.
Zoo ntawm hiav txwv thiab dej hiav txwv nthwv dej
Thaum mus txog ntawm ntug dej, hiav txwv nthwv dej nce ntxiv nrog kev hloov pauv hauv qhov tob. Qee zaum lawv ncav cuag qhov siab ntawm ob peb meters. Nyob rau lub sijhawm zoo li no, lub zog kinetic ntawm cov dej loj loj tau xa mus rau cov teeb meem ntawm ntug hiav txwv, uas tau raug puas tsuaj sai sai hauv nws cov cawv. Lub zog ntawm nthwv dej qee zaum nce mus txog qhov muaj txiaj ntsig zoo.
Elastic waves
Hauv kev siv tshuab, tsis yog tsuas yog kev vibrations ntawm cov kua dej xwb, tab sis kuj tseem hu ua elastic nthwv dej. Cov no yog perturbations uas propagate nyob rau hauv sib txawv xov xwm nyob rau hauv qhov kev txiav txim ntawm elastic zog nyob rau hauv lawv. Xws li ib tug perturbation yog ib qho kev sib txawv ntawm cov khoom ntawm ib qho nruab nrab muab los ntawm txoj hauj lwm sib npaug. Ib qho piv txwv zoo ntawm elastic nthwv dej yog ib txoj hlua ntev los yog roj hmab raj txuas rau ib yam dab tsi ntawm ib qho kawg. Yog tias koj rub nws nruj, thiab tom qab ntawd ua kom muaj kev cuam tshuam ntawm nws qhov thib ob (tsis kho) kawg nrog lub ntsej muag ntse, koj tuaj yeem pom tias nws "khiav" li cas rau tag nrho txoj hlua ntev mus rau kev txhawb nqa thiab rov qab los.
Source of mechanical nthwv dej
Qhov kev cuam tshuam thawj zaug ua rau pom cov nthwv dej hauv nruab nrab. Nws yog tshwm sim los ntawm kev ua ntawm qee lub cev txawv teb chaws, uas nyob rau hauv physics hu ua qhov chaw ntawm nthwv dej. Nws tuaj yeem yog txhais tes ntawm tus neeg viav vias hlua, lossis pebble pov rau hauv dej. Nyob rau hauv rooj plaub thaum qhov kev txiav txim ntawm qhov chaw yog luv luv, ib tug yoj ib leeg feem ntau tshwm nyob rau hauv nruab nrab. Thaum "kev cuam tshuam" ua rau ntev oscillatory txav, nthwv dej pib tshwm ib tom qab.
Cov xwm txheej rau qhov tshwm sim ntawm cov tshuab tsis muaj zog
Kev oscillation no tsis yog ib txwm tsim. Ib qho xwm txheej tsim nyog rau lawv qhov tsos yog qhov tshwm sim ntawm lub sijhawm ntawm kev cuam tshuam ntawm nruab nrab ntawm cov rog tiv thaiv nws, tshwj xeeb, elasticity. Lawv nyiam coj cov neeg nyob sib ze los ze zog ua ke thaum lawv txav mus deb, thiab thawb lawv tawm ntawm ib leeg thaum lawv los ze zog. Elastic rog ua nyob deb ntawmqhov chaw ntawm perturbation ntawm particle, pib coj lawv tawm ntawm qhov sib npaug. Nyob rau tib lub sijhawm, tag nrho cov khoom ntawm qhov nruab nrab yog koom nrog hauv ib qho oscillatory motion. Kev nthuav tawm ntawm cov oscillations yog nthwv dej.
Mechanical nthwv dej hauv qhov nruab nrab elastic
Nyob rau hauv yoj elastic, muaj 2 hom kev txav ib txhij: particle oscillations thiab perturbation propagation. Ib tug longitudinal yoj yog ib tug neeg kho tshuab nthwv dej uas nws hais oscillate raws cov kev taw qhia ntawm nws propagation. Lub transverse nthwv dej yog nthwv dej uas nws cov khoom nruab nrab oscillate hla cov kev taw qhia ntawm nws qhov kev nthuav tawm.
Cov khoom ntawm cov tshuab tsis muaj zog
Kev cuam tshuam hauv cov nthwv dej ntev yog qhov tsis tshua muaj kev cuam tshuam thiab compression, thiab nyob rau hauv ib lub nthwv dej transverse lawv yog kev hloov pauv (tshem tawm) ntawm qee cov txheej txheem nruab nrab ntawm lwm tus. Lub compression deformation yog nrog los ntawm cov tsos ntawm elastic zog. Nyob rau hauv cov ntaub ntawv no, shear deformation yog txuam nrog cov tsos ntawm elastic zog tshwj xeeb tshaj yog nyob rau hauv cov khib nyiab. Nyob rau hauv gaseous thiab kua xov xwm, qhov kev hloov ntawm cov khaubncaws sab nraud povtseg ntawm cov xov xwm no tsis yog nrog los ntawm cov tsos ntawm lub zog hais. Vim lawv cov khoom, cov nthwv dej ntev tuaj yeem nthuav tawm hauv txhua qhov xov xwm, thaum cov nthwv dej hla tuaj yeem nthuav tawm tsuas yog hauv cov khib nyiab.
Nthuav nthwv dej ntawm cov kua dej
Nkoj ntawm cov kua dej tsis yog qhov ntev lossis hloov pauv. Lawv muaj ib tug complex, thiaj li hu ua longitudinal-transverse cim. Hauv qhov no, cov kua dej txav mus rau hauv lub voj voog lossis raws elongated ellipses. Lub voj voog ncig ntawm cov khoom nyob rau saum npoo ntawm cov kua, thiab tshwj xeeb tshaj yog thaum lub sij hawm loj oscillations, nrog rau lawv qeeb tab sis tas li.tsiv nyob rau hauv cov kev taw qhia ntawm yoj propagation. Nws yog cov khoom ntawm cov tshuab tsis muaj zog hauv dej uas ua rau pom ntau yam nqaij nruab deg ntawm ntug dej.
Mechanical yoj zaus
Yog hais tias nyob rau hauv ib qho nruab nrab elastic (kua, khoom, gaseous) kev co ntawm nws cov hais yog zoo siab, ces vim yog kev sib cuam tshuam ntawm lawv, nws yuav propagate nrog ib tug ceev u. Yog li, yog hais tias lub cev oscillating nyob rau hauv ib tug gaseous los yog kua nruab nrab, ces nws lub zog yuav pib kis mus rau tag nrho cov hais nyob ib ncig ntawm nws. Lawv yuav koom nrog cov tom ntej hauv cov txheej txheem thiab lwm yam. Nyob rau hauv rooj plaub no, kiag li tag nrho cov ntsiab lus ntawm qhov nruab nrab yuav pib oscillate nrog tib zaus, sib npaug rau zaus ntawm lub cev oscillating. Nws yog qhov zaus ntawm nthwv dej. Hauv lwm lo lus, tus nqi no tuaj yeem ua tus cwj pwm li oscillation zaus ntawm cov ntsiab lus nyob rau hauv nruab nrab qhov twg yoj propagates.
Nws yuav tsis paub meej tam sim ntawd qhov txheej txheem no tshwm sim li cas. Mechanical nthwv dej yog txuam nrog kev hloov ntawm lub zog ntawm oscillatory motion los ntawm nws qhov chaw mus rau qhov nruab nrab ntawm qhov nruab nrab. Yog li ntawd, thiaj li hu ua periodic deformations tshwm sim, uas yog nqa los ntawm nthwv dej ntawm ib qho mus rau lwm qhov. Nyob rau hauv cov ntaub ntawv no, qhov hais ntawm nruab nrab lawv tus kheej tsis txav nrog lub nthwv dej. Lawv oscillate nyob ze lawv txoj hauj lwm equilibrium. Tias yog vim li cas qhov kev nthuav tawm ntawm lub tshuab hluav taws xob tsis yog nrog kev hloov ntawm cov teeb meem ntawm ib qho mus rau lwm qhov. Mechanical waves muaj ntau zaus. Yog li ntawd, lawv tau muab faib ua ntau yam thiab tsim cov nplai tshwj xeeb. Zaus yog ntsuas hauv hertz (Hz).
Basic Formulas
Mechanical yoj, uas nws cov qauv kev suav yog qhov yooj yim heev, yog ib qho khoom zoo rau kev kawm. Lub nthwv dej nrawm (υ) yog qhov ceev ntawm nws txoj kev txav mus rau pem hauv ntej (qhov chaw ntawm txhua lub ntsiab lus uas lub oscillation ntawm nruab nrab tau mus txog lub sijhawm):
υ=√G/ ρ, qhov twg ρ yog qhov ntom ntawm qhov nruab nrab, G yog qhov qauv ntawm elasticity.
Thaum xam, tsis txhob cuam tshuam qhov nrawm ntawm lub tshuab hluav taws xob hauv nruab nrab nrog qhov nrawm ntawm kev txav ntawm cov khoom nruab nrab uas koom nrog hauv cov txheej txheem nthwv dej. Yog li, piv txwv li, lub suab nthwv dej hauv huab cua nthuav tawm nrog qhov nruab nrab vibrational ceev ntawm nws cov molecules ntawm 10 m / s, thaum lub suab nrov nthwv dej hauv ib txwm muaj 330 m / s.
Wave pem hauv ntej los ntawm ntau hom, qhov yooj yim tshaj plaws yog:
• Spherical - tshwm sim los ntawm kev hloov pauv hauv cov pa roj lossis kua nruab nrab. Nyob rau hauv cov ntaub ntawv no, lub amplitude ntawm nthwv dej txo nrog kev ncua deb ntawm qhov chaw nyob rau hauv inverse proportions mus rau lub square ntawm qhov kev ncua deb.
• Flat - yog ib lub dav hlau uas nyob rau ntawm qhov kev taw qhia ntawm nthwv dej propagation. Nws tshwm sim, piv txwv li, nyob rau hauv lub piston lub tog raj kheej kaw thaum nws oscillates. Lub dav hlau nthwv dej yog tus cwj pwm los ntawm qhov yuav luag tas li amplitude. Nws qhov txo qis me ntsis nrog kev ncua deb ntawm qhov kev cuam tshuam yog cuam tshuam nrog qib ntawm viscosity ntawm gaseous lossis kua nruab nrab.
wavelength
Nyob rau hauv lub wavelength yog to taub qhov kev ncua deb uas nws pem hauv ntej yuav txav mus rau lub sij hawm ntawdsib npaug lub sij hawm ntawm oscillation ntawm qhov nruab nrab:
λ=υT=υ/v=2πυ/ ω, qhov twg T yog lub sijhawm oscillation, υ yog nthwv dej nrawm, ω yog lub voj voog zaus, ν yog oscillation zaus ntawm cov ntsiab lus nruab nrab.
Vim tias kev nthuav tawm ceev ntawm lub tshuab hluav taws xob yog nyob ntawm qhov khoom nruab nrab, nws qhov ntev λ hloov pauv thaum hloov pauv ntawm ib qho nruab nrab mus rau lwm qhov. Hauv qhov no, qhov zaus oscillation ν yeej ib txwm zoo ib yam. Mechanical thiab electromagnetic nthwv dej zoo ib yam li thaum lawv nthuav tawm, lub zog raug xa mus, tab sis tsis muaj teeb meem pauv.
