2 Vibrations and Waves “Wiggles in Time” “Wiggles in Space” Water Waves Sound WavesLight WavesOar in WaterWings of a BeeElectrons in an Light Bulb
3 Vibrations and Waves Waves transmit energy and information. Sound and Light are both waves.
4 Simple Harmonic Motion... …is to-and-fro vibratory motion....results in sine curves.Examples:metronomemass on a springpendulum
5 Forces and vibrations Vibration - repetitive back and forth motion At the equilibrium position, spring is not compressedWhen disturbed from equilibrium position, restoring force acts toward equilibriumCarried by inertia past equilibrium to other extremeExample of “simple harmonic motion”
6 Describing vibrations Amplitude - maximum extent of displacement from equilibriumCycle - one complete vibrationPeriod - time for one cycleFrequency - number of cycles per second (units = hertz, Hz)Period and frequency inversely related
7 Description Period - the time required for one vibration measured in secondsFrequency - number of vibrations per unit timemeasured in HertzBowling Ball Example
9 Pendulums & Galileo The period does not depend on the amount of mass. The period does depend on the length of the pendulum.
10 * Example Test Question: If you double the frequency of a vibrating object, what happens to the period?a) the period doublesb) the period stays the samec) the period is cut in half d) not enough information is givento answer this question.
11 Example Question*Changing which of the following affects the period of a pendulum?a) massb) amplitudec) lengthd) angle
12 What is the frequency in vibrations per second of a 60-Hz wave? Answer: 60 cycles per secondWhat is its period?Answer: 1/60 second
13 Waves Periodic (traveling) disturbances transporting energy Causes Periodic motion disturbing surroundingsPulse disturbance of short durationMechanical wavesRequire medium for propagationWaves move through mediumMedium remains in place
14 Wave Motion Waves Medium medium - the stuff that carries the wave water waveswaterwaves on a roperopestadium wavespeoplesoundairlightspace (vacuum)
15 Wave Speed... the speed with which waves pass by a particular point e.g. the speed of a surferIt depends only on the type of medium.Wave Speed = Frequency WavelengthWaves on a RopeTable in Notes – Appearance, Node, Antinodes, Wavelength, Frequency
16 Describing waves Graphical representation Pure harmonic waves = sines or cosinesWave terminologyWavelengthAmplitudeFrequencyPeriodWave propagation speed
17 Example Test Questions Answer these questions using the sine wave provided. What is the amplitude of the wave?What is its wavelength?How many nodes are there?
18 Example Wave2 ½ meters20 cmAmplitude = 10 cmWavelength = 1 mNumber of Nodes = 6
19 If a water wave oscillated up and down three times each second and the distance between wave crest is 2 m, what is its frequency?Answer: 3 HzWhat is its period?Answer: 1/3 secondWhat is its wavelength?Answer: 2 mWhat is its wave speed?Answer: 6 m/s
20 Kinds of waves, cont. Transverse waves Vibration direction perpendicular to wave propagation directionExample: plucked stringSolids - support both longitudinal and transverse wavesSurface water wavesCombination of bothParticle motion = circular
21 Kinds of waves Longitudinal waves Vibration direction parallel to wave propagation directionParticles in medium move closer together/farther apartExample: sound wavesGases and liquids - support only longitudinal waves
22 Waves in air Longitudinal waves only Large scale - swinging door creates macroscopic currentsSmall scale - tuning fork creates sound wavesSeries of condensations (overpressures) and rarefactions (underpressures)
23 INTERFERENCEConstructive or destructive interference results when waves add.Standing Waves - wave pattern produced from interfering wavesExamplesVibrating Strings in LabOrgan Pipe in LabBell Wave Machine in Class
25 DOPPLER EFFECT the change in wavelength due to motion of the source "Wheeeeeeeeeeee…….Oooooooooooooo”Examples:moving cars and trainsmoving buzzer in a nerf ball (in class)rotating whistleDraw Doppler Picture
26 Sounds from moving sources Doppler effectWave pattern changed by motion of source or observerApproaching - shifted to higher frequencyReceding - shifted to lower frequencySupersonic speed - shock wave and sonic boom produced
28 Question 1*A train whistle at rest has a frequency of 3000 Hertz. If you are standing still and observe the frequency to be 3010 Hertz, then you can conclude that...a) the train is moving away from you.b) the train is moving toward youc) the sound from the whistle has echoedd) not enough information is given
29 Question 2*Dipping a finger in water faster and faster causes the wavelength of the spreading waves toa) increaseb) decreasec) stay the samed) not enough information is given
30 Question 3*The distance from trough to trough on a periodic wave is called its...a) frequency.b) period.c) wavelength.d) amplitude.
31 Sound... ...a longitudinal wave in air caused by a vibrating object. Sound requires a medium.solid, liquid or gasSound waves have compression and rarefaction regions.
32 Nature of Sound in Air Sound requires a medium. solid, liquid or gasDemo: Bell in a evacuated Bell JarSound waves have compression and rarefaction regions.
33 Sound infrasonic ultrasonic human hearing range frequencies < 20 Hz frequencies between 20 Hz and 20,000 Hz
34 Sound waves Require medium for transmission Speed varies with Inertia of moleculesInteraction strengthTemperatureVarious speeds of sound
35 Velocity of sound in air Varies with temperatureWarmer the air, greater the kinetic energy of the gas moleculesMolecules of warmer air transmit sound impulses from molecule to molecule more rapidlyGreater kinetic energy sound impulse transmitted fasterIncrease factor (units!):0.6 m/s/°C; 2.0 ft/s/°C
36 SPEED OF SOUND How it varies: increases with humidity increases with temperatureincreases with density
38 What is the approximate distance of a thunderstorm when you note a 3 second delay between the flash of the lightning and the sound of the thunder?Answer: 3 seconds 340 meters/second= 1020 metersSee blue questions on page 345.*
39 Sources of sound Vibrating objects Source of all sound Irregular, chaotic vibration produces noiseRegular, controlled vibration can produce musicAll sound is a combination of pure frequencies
40 Vibrating strings Important concepts - strings with fixed ends More than one wave can be present at the same timeWaves reflected and inverted at end pointsInterference occurs between incoming and reflected waves
41 Vibrating strings, cont. Standing wavesProduced by interferences at resonant frequenciesNodes - destructive interference pointsAnti-nodes - points of constructive interference
42 Resonant frequencies of strings Fundamental - lowest frequencyHigher modes - overtones (first, second, …)Mixture of fundamental and overtones produces “sound quality” of instrumentFormula for resonant frequencies