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)

25.7 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 Physlets 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