Chapter 25Vibrations & Waves
Conceptual Physics1999 Hewitt
Bloom High School
DefinitionsVibration- a wiggle in
timeAtoms
Wave- a wiggle in space and timeEarthquakes, water,
sound, etc.
25.1 Vibration of a PendulumPeriod, T (s)- time required for
one complete cycleBack and forth
Two pendulums of the same length have the same period, regardless of massLonger pendulum string- longer
TShorter string, shorter T
25.2 Wave DescriptionSimple Harmonic Motion (SHM)- back-and-forth
motion vibratory motion
Sine curve- shape traced out when a pendulum is followedP. 373 Figure 25.2Physics Physlets P.16.9 (Animation 3)Wave on a String Phet
Frequency, f (Hertz, Hz)- number of cycles per secondInverse relationship to period (T)f=1/T and T=1/f
Sine WavesCrest- top-most portion
of a waveTrough- bottom-most
portion of a waveAmplitude (A)- vertical
distance measured from equilibrium to a crest
Wavelength (l)- horizontal distance from crest-to-crest or trough-to-trough
25.3 Wave MotionEnergy transfer with a medium
Energy is transferred by a disturbance in the medium, not the particles in the medium moving
Sound- compression of air molecules in wavesEarthquake- compression of Earth or rise-and-fall of
Earth
Energy can be transferred without a mediumLight- oscillation of electromagnetic energy
As well as X-rays, infrared, microwaves, FM, AM, etc.
25.4 Wave SpeedRegardless of medium, wavelength and frequency
are neededSpeed = distance ÷ timeSpeed = wavelength ÷ period = wavelength •
frequencyv = l/T = l • f
Speed of sound in air ranges from 340-350 m/sTemperature dependant
25.5 Transverse WavesTransverse waves- motion of the medium moves
perpendicularly to the direction the energy travelsRopes, surface water waves, stringed instrumentsElectromagnetic wavesPhysics Physlets I.17.1 (Animation 1 & 2)
25.6 Longitudinal WavesLongitudinal waves- motion of the medium
moves parallel to the direction the energy travelsSlinky pulled backPhysics Physets I.17.1 (Animation 3)
25.6 InterferenceInterference pattern- waves from two separate
sources overlapping
Constructive interference- the crest of one wave overlaps with the crest of another waveIn Phase- Increases amplitudePhysics Physlet I.17.3 (Animation 1)
Destructive interference- the crest of one wave overlaps with the trough of another waveOut of Phase- Decreases amplitudePhysics Phslets I.17.3 (Animation 2)
Interference Pattern
25.8 Standing WavesStanding waves- when the incident and reflected
waves overlap
Nodes- the portion of the waves that remain stationary
Antinodes- the portion of the waves that have the largest disturbance
http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave4.html
25.9 Doppler EffectDoppler Shift- change in frequency due to motion
between the sound source and receiverPhysics Physlet I.18.4 (Animation 4)Motion only depends on the objects getting closer or
further away. It doesn’t matter who does which.Blue Shift
Source stationary, receiver moving towards source Receiver stationary, source moving towards receiver
Red Shift Source stationary, receiver moving away from source Receiver stationary, source moving away from receiver
Doppler Shift (Sound & Light)
25.10 Bow WavesBow waves-
Constructive interference in water as created by an object moving faster than the waters’ speed2D wave
25.11 Shock WavesShock waves-
Constructive interference in air as created by an object moving faster than the speed of sound3D wave
Sonic Boom- increased amplitude of so many waves arriving at our ears all at one timePhysics Physlet I.18.4
(Animation 5)
Terms (lots of ‘em)AmplitudeAntinodesBlue shiftBow waveConstructive interferenceCrestDestructive interferenceDoppler effectFrequencyHertzIn phaseInterference patternLongitudinal waveNode
Out of phasePeriodRed shiftShock waveSimple harmonic motionSine curveSonic boomStanding waveTransverse waveTroughVibrationWaveWavelength
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