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WAVES AND VIBRATIONS NOTES
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A wave is a vibration moving in time and space
It cannot exist in one place but must
extend from one place to another
Wave motion is a wa to trans!er energ wit"out
transfer of matter
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A vibration is back and forth movement
A single #isturbance or vibration is a wave pulse
I! t"e source repeate#l vibrates it pro#uces periodic motion
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Sound is pro#uce# w"en matter vibrates
Demonstration$ W"at "appens w"en a tuning !or%
is place# in water&
Since soun# is pro#uce# w"en matter vibrates'
soun# is a !orm o! mechanical energ(
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)rest
troug"
mi#point
)rest$ High point in the wave
Troug"$ Low point in the wave
********+i#point o! wave where the wave is in equilibrium
Amplitu#e Distance from the midpoint to the crest or trough
T"e "ig"er t"e amplitu#e t"e stronger the wave
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Wavelengt" is$ the distance from one point on the wave to
the identical point on the next wave.
Crest to Crest, or trough to trough
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,re-uenc is$ How frequentl a vibration occurs.
How man wavelengths or wave ccles pass in one second.
I! . wavelengt"s /or vibrations' or wave ccles0 pass a
point in one secon#' t"en t"e !re-uenc is$! vibrations" second. #$r ! ccles" sec%
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1ert2 is$ a unit of frequenc #abbreviated H&%
It was name# a!ter
1einric" 1ert2
w"o #emonstrate#
ra#io waves in 3445(
One vibration per secon# is one 1ert2(
. vibrations /or waves' or ccles0 per
secon# is ________ 1ert2 2
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DE+ONSTRATIONS$
Hacksaw blade$ /hold blade against table edge.Change length hanging over and vibrate it.
Describe t"e !re-uenc o! vibration an# pitc"
/"ig"ness or lowness o! t"e soun#0 w"en t"e "ac%saw bla#e is long(
Longer vibrations, so lower sound Describe t"e !re-uenc o! vibration an# pitc" w"en t"e
"ac%saw bla#e is s"orter(
Higher vibrations so higher pitch
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Containers with water( /pop bottles
to blow across or crstal glass to rub
!inger aroun#0
W"at is t"e relations"ip between t"e amount o! water
in eac" container an# t"e pitc"&
Less water vibrating means higher pitch.
'ore water vibrating is lower pitch
T"e longer t"e lengt" o! vibrating air above t"e water'
t"e Lower t"e pitc" when blowing into a bottle
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I! a wave6s !re-uenc is %nown' t"en ou can calculate
t"e period o! time it ta%es !or one wave to pass(
I! t"e !re-uenc is . 12' t"en t"e time it ta%es !or
3 vibration is ( second (
Explain t"e relations"ip between 7erio# an# ,re-uenc$
)requenc * + eriod * +
eriod #-% )requenc t is an inverse relationship
f freq * / H& then eriod * +"/ or .! seconds
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T"e Sears Buil#ing in
)"icago swas bac% an# !ort"
at a vibration !re-uenc o! 8(3 12(W"at is its 7erio# o! vibration&
- * + " f
+ " 0.+ ccles"sec * +0 seconds"ccle
t takes +0 seconds for it to swa back
and forth one time
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WAVE S7EED
Spee# o! a wave #epen#s on t"e me#iumt"roug" w"ic" t"e wave travels(
Spee# #epen#s on$
3( Densit o! materials how man molecules there
are to bump into each other .( Elasticit how well it changes shape and then
springs back. 'ore elastic, the faster the
waves travel.
9( Temperature higher the temperature,
the faster the molecules move
Soun# travels about 998 m:s * 9;8 m:s #epen#ing on t"e temperature o!
t"e air( It travels < times !aster in water' an# 3; times !aster in steel(
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Wave Spee# = frequenc x wavelength
λ 1reek letter Lambda * wavelength
Wave Speed Freq. λ
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Soun# Waves
,re-uenc /120 Wavelengt" /m0 Wave Spee# /m:s0358 .(39 9 95 8(45 9
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I! a water wave vibrates up an# #own . times eac"
secon# an# t"e #istance between wave crests is 3(; meters'
w"at is t"e !re-uenc o! t"e wave&
W"at is its wavelengt"& W"at is its spee#&
) * ! H& 2avelength * +./ m
Speed * ! ccles x +./ m = 3 m"sec
Sec Ccle
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W"at is t"e wavelengt" o! a 9
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TRANSVERSE WAVES
'otion of the wave is at right angles to the direction of travel
Examples$ waves on the surface of liquids,
8adio waves, light waves
slink demo
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?ON@ITDINA? WAVES
motion of waves is in the same direction
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Examples$ sound waves
SM!" #$%&S
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'ransverse
(ongit)dinal
co*pression
rare+action
S #"-$"W F 'H" W-" '/"S
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NATRA? ,REEN)C$
W"en ou #rop a wrenc" an# baseball bat on t"e
!loor' ou "ear . #i!!erent soun#s( T"e vibrate#i!!erentl( W"en an obect compose# o! an elastic
material is #isturbe# it vibrates at its own special set
o! !re-uencies( T"is nat)ral +req)enc0 #epen#s on
!actors suc" as$
elasticit and the shape of the ob9ect
RESONAN)E$
W"en t"e vibration o! one obect causes anot"er obect to$
vibrate at its natural frequenc
A #ramatic increase in :mplitude occurs(
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Examples o! Resonance
Swinging on a swing pump in
rhthm with natural frequenc of theswing, go higher and higher
Tuning !or% can cause another to vibrate
Tacoma Narrows Bri#ge
destroed b a 40 mph wind (video)
Wine glass s"attering
http://www.acoustics.salford.ac.uk/feschools/waves/wine1video.htmhttp://www.acoustics.salford.ac.uk/feschools/waves/wine1video.htm
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$%'"#F"#"%C" F W-"S
)onstructive Inter!erence$ when one wave crestoverlaps another crest and the build together
Animation courtes o! Dr( Dan Russell' ettering niversit
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Destructive Inter!erence$ when one wave crest
overlaps a trough and the cancel each other out.
;S
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SHW M$#" /''"#%S
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Stan#ing Waves$ when wave is reflected back
exactl opposite to the original wave
A = anti*no#e B = no#e
Animation courtes o! Dr( Dan Russell' ettering niversit
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Beats$ periodic variation in loudness of sounds
caused when ! slightl different frequencies are
sounded together
I! one tuning !or% vibrates at .5< 1ert2' an# t"e
ot"er at .5. 1ert2' t"en t"e are Fin stepG . times
eac" secon#( A beat !re-uenc o! 2 h1 is "ear#(
Animation courtes o! Dr( Dan Russell' ettering niversit
#emo
http://library.thinkquest.org/19537/java/Beats.htmlhttp://library.thinkquest.org/19537/java/Beats.html
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T1E DO77?ER E,,E)T$
T"e Doppler e!!ect is a c"ange in frequenc of a
wave due to the motion of the source or receiver.
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Doppler E!!ect occurs !or visible lig"t too(
S"ort lig"ts waves are >lue an#
?ong wavelengt"s are 8ed
Astronomers can measure w"et"er stars an# galaxies are
moving towar# us or awa !rom us b loo%ing at t"e
lig"t s"i!t(
Blue S"i!t means * the light is coming faster ?
stars are moving forward
Re# S"i!t means* the star is going awa
T"e can calculate t"e spee# o! a spinning star(
T"ere is a blue s"i!t on t"e si#e spinning towar# us
an# a re# s"i!t on t"e si#e spinning awa(
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7olice use t"e Doppler e!!ect o! ra#ar to #etermine
t"e spee# o! a car( A computer in t"e ra#ar guncompares t"e !re-uenc o! t"e ra#ar emitte# b
t"e antenna wit" t"e
frequenc of the reflected waves.
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OS)I??OS)O7E$ : device that is used to measureelectrical signals as waves. t shows the strength of the
wave #amplitude% and the period of time between
each wave. @ou can then calculate the frequenc
of the waves