Chapter 25Chapter 25
Vibrations and Vibrations and WavesWaves
Vibrations and WavesVibrations and Waves
Waves transmit Waves transmit energyenergy and and informationinformation..
SoundSound and and LightLight are both waves. are both waves.
Simple Harmonic MotionSimple Harmonic Motion
to-and-fro vibratory motionto-and-fro vibratory motion
results in sine curvesresults in sine curves Examples: Examples:
– Metronome Metronome
Simple Harmonic MotionSimple Harmonic Motion
to-and-fro vibratory motionto-and-fro vibratory motion
results in sine curvesresults in sine curves Examples: Examples:
– mass on a springmass on a spring
Simple Harmonic MotionSimple Harmonic Motion
to-and-fro vibratory motionto-and-fro vibratory motion
results in sine curvesresults in sine curves Examples: Examples:
– pendulumpendulum
PendulumsPendulums The period The period does notdoes not depend on the amount depend on the amount
of mass.of mass.
The period The period doesdoes depend on the length of the depend on the length of the pendulum.pendulum.
T l g2
Wave ComparisonsWave Comparisons
Water WavesWater Waves Sound WavesSound Waves Light WavesLight Waves
– WavesWaves– MediumMedium– Wave SpeedWave Speed– What if you go faster?What if you go faster?– Human PerceptionHuman Perception
Vibrations and WavesVibrations and Waves
Oar in WaterOar in Water Wings of a BeeWings of a Bee Electrons in an Electrons in an
Light BulbLight Bulb
Water WavesWater Waves Sound WavesSound Waves Light WavesLight Waves
“Wiggles in Time” “Wiggles in Space”
Wave DescriptionWave Description
PeriodPeriod - the time required for one vibration - the time required for one vibration
» measured in secondsmeasured in seconds
FrequencyFrequency - number of vibrations per unit time - number of vibrations per unit time
» measured in Hertzmeasured in Hertz
Bowling Ball Demo
Wave DescriptionWave Description
Bowling Ball Demo
FrequencyPeriod
1
PeriodFrequency
1
Example Test Question:Example Test Question:
If you double the frequency of a vibrating If you double the frequency of a vibrating object, what happens to the period?object, what happens to the period?
a) the period doublesa) the period doubles
b) the period stays the sameb) the period stays the same
c) the period is cut in halfc) the period is cut in half d) d) not enough information is given not enough information is given
to answer this question.to answer this question.
What is the frequency in vibrations What is the frequency in vibrations per second of a 60-Hz wave?per second of a 60-Hz wave?
Answer: 60 cycles per secondAnswer: 60 cycles per second
What is its period?What is its period?Answer: 1/60 secondAnswer: 1/60 second
Sine CurvesSine Curves
AmplitudeAmplitude - distance from the baseline to - distance from the baseline to the crest of a wavethe crest of a wave
WavelengthWavelength - the distance from the top of - the distance from the top of one crest to the top of the next oneone crest to the top of the next one
2 ½ meters
20 cm
Wavelength = 1 m
Example Wave
Amplitude = 10 cm
Number of Nodes = 6
Antinode
Wave MotionWave Motion mediummedium - the stuff that carries the wave - the stuff that carries the wave
Waves Mediumwater waves water
waves on a rope rope
stadium waves people
sound air
light space (vacuum)
Wave SpeedWave Speed the speed with which waves pass by a the speed with which waves pass by a
particular pointparticular point» e.g. the speed of a surfere.g. the speed of a surfer
depends only on the type of depends only on the type of mediummedium
Wave Speed = Frequency Wave Speed = Frequency Wavelength Wavelength
Waves on a Rope
If a water wave oscillated up and down If a water wave oscillated up and down three times each second and the distance three times each second and the distance between wave crest is 2 m, what is its between wave crest is 2 m, what is its frequency?frequency?
Answer: 3 HzAnswer: 3 HzWhat is its period?What is its period?
Answer: 1/3 secondAnswer: 1/3 secondWhat is its wavelength?What is its wavelength?
Answer: 2 mAnswer: 2 mWhat is its wave speed?What is its wave speed?
Answer: 6 m/sAnswer: 6 m/s
Wave ComparisonsWave Comparisons
Water WavesWater Waves Sound WavesSound Waves Light WavesLight Waves
– WavesWaves– MediumMedium– Wave SpeedWave Speed– What if you go faster?What if you go faster?– Human PerceptionHuman Perception
Shock WaveShock Wave
- slower than the speed of soundSubsonicSubsonic
Supersonic - faster than the speed of sound
Mach Number =speed of soundspeed of object
Transverse WavesTransverse Waves side to side vibration in a direction side to side vibration in a direction
perpendicular to the wave's motion perpendicular to the wave's motion
Examples: Examples: – water waveswater waves– waves on a ropewaves on a rope– string musical instrumentsstring musical instruments
Longitudinal WavesLongitudinal Waves back and forth vibration in a direction back and forth vibration in a direction
parallel to the wave's motion parallel to the wave's motion
Examples: Examples: – slinky wavesslinky waves– sounds waves (vortex box)sounds waves (vortex box)
http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
Example QuestionExample Question
The distance from trough to trough on a The distance from trough to trough on a periodic wave is called its...periodic wave is called its...
– a) frequency.a) frequency.– b) period.b) period.– c) wavelength.c) wavelength.– d) amplitude.d) amplitude.
Example QuestionExample Question
Changing which of the following affects the Changing which of the following affects the period of a pendulum?period of a pendulum?
– a) massa) mass– b) amplitudeb) amplitude– c) lengthc) length– d) angled) angle
Example QuestionExample Question
Dipping a finger in water faster and faster causes Dipping a finger in water faster and faster causes the wavelength of the spreading waves tothe wavelength of the spreading waves to
– a) increasea) increase– b) decreaseb) decrease– c) stay the samec) stay the same– d) not enough information is givend) not enough information is given
INTERFERENCEINTERFERENCE ConstructiveConstructive or or destructivedestructive interference interference
results when waves add.results when waves add.
Standing WavesStanding Waves - wave pattern produced - wave pattern produced from interfering wavesfrom interfering waves– ExamplesExamples
» Rope WavesRope Waves» Vibrating Strings in LabVibrating Strings in Lab» Guitar StringsGuitar Strings» Bell Wave MachineBell Wave Machine» Organ PipeOrgan Pipe
http://www.kettering.edu/~drussell/Demos/superposition/superposition.html
DOPPLER EFFECTDOPPLER EFFECT the change in frequency due to motion of the the change in frequency due to motion of the
source source
"Wheeeeeeeeeeee…….Oooooooooooooo”"Wheeeeeeeeeeee…….Oooooooooooooo”
Examples:Examples:– moving cars and trainsmoving cars and trains– moving buzzer in a nerf ball (in class)moving buzzer in a nerf ball (in class)– rotating whistle rotating whistle
Doppler with Water
Doppler Shift Gives Radial Doppler Shift Gives Radial VelocityVelocity
Radar
True Velocity
Tangential Velocity
Radial Velocity
Example QuestionExample Question
A train whistle at rest has a frequency of A train whistle at rest has a frequency of 3000 Hertz. If you are standing still and 3000 Hertz. If you are standing still and observe the frequency to be 3010 Hertz, then observe the frequency to be 3010 Hertz, then you can conclude that...you can conclude that...
– a) the train is moving away from you.a) the train is moving away from you.– b) the train is moving toward youb) the train is moving toward you– c) the sound from the whistle has echoedc) the sound from the whistle has echoed– d) not enough information is givend) not enough information is given
Example QuestionExample Question
Changing which of the following affects the Changing which of the following affects the period of a pendulum?period of a pendulum?– a) massa) mass– b) amplitudeb) amplitude– c) lengthc) length– d) angled) angle
Example QuestionExample Question
Dipping a finger in water faster and faster Dipping a finger in water faster and faster causes the wavelength of the spreading waves causes the wavelength of the spreading waves toto
– a) increasea) increase– b) decreaseb) decrease– c) stay the samec) stay the same– d) not enough information is givend) not enough information is given
Example QuestionExample Question
The distance from trough to trough on a The distance from trough to trough on a periodic wave is called its...periodic wave is called its...
– a) frequency.a) frequency.– b) period.b) period.– c) wavelength.c) wavelength.– d) amplitude.d) amplitude.
Example QuestionExample Question
Dipping a finger in water faster and faster Dipping a finger in water faster and faster causes the wavelength of the spreading causes the wavelength of the spreading waves towaves to
– a) increasea) increase
– b) decreaseb) decrease
– c) stay the samec) stay the same
– d) not enough information is givend) not enough information is given
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