2Waves Definition of wave A disturbance that transfers energy through matter or space“Disturbance”-a change from a normal state
3Periodic or Harmonic Motion Motion that repeats itself in the same amount of timeOne repetition of motion called a cycleExamples?What does graph look like?
4Periodic or Harmonic Motion Amount of time to complete cycle called a period (T)Frequency (f) is how many complete cycles occur in one secondT = 1/f or f =1/TAmplitude is the amount of displacement from rest
19Represent longitudinal waves as transverse waves Particle displacement in a longitudinal wave can be graphed as a transverse waveParticle motion from rest graphed as amplitude
20Sound Waves Sound waves move vibrational energy through matter Sound waves are longitudinal waves
21Wave Properties Common Characteristics of Wave LengthHeightFrequency (how often they occur)Period (how long to make 1 cycle)SpeedAll Characteristics of Waves Can Vary
22Wave CharacteristicsWavelength (λ)-the distance between repeating parts of a waveTrough to troughPeak to PeakRarefaction to RarefactionCompression to compression- Or any other repeating part
23Wave CharacteristicsWave amplitude (height)-the maximum displacement from the undisturbed position of the medium to the top of a crest or bottom of a trough
24Check Your Understanding Transverse Waves The wavelength of the wave in the diagram above is given by letter ______.The amplitude of the wave in the diagram above is given by letter _____.
25Check Your Understanding Transverse Waves Indicate the interval which represents one full wavelength.
26Wave CharacteristicsThe frequency (f) of a wave is the number of complete waves (cycles) that pass the observer in a given time.Hertz is the unit of frequency, and just means how many cycles (peaks) per second.
27Wave CharacteristicsThe period (T) of a wave is the time for a wave to make one complete cycle (peak to peak).The period is related to the frequency by the following equation f=1/T
28Wave CharacteristicsThe speed (v) of a wave is the how fast the wave is movingdistance the wave travels in a certain amount of time.
29Wave CharacteristicsThe relationship between the speed, frequency, period and wavelengthExample:2 waves each second (i.e. frequency = 2 Hz)the period is equal to 1/f = ½ secondthe distance between the waves as 25 cm: this is the wavelength.In 0.5 s, waves move 25 cm, so we can find the speed using:speed= v = λ x f = 25 x 2 = 50 cm/sec ORspeed = v = λ x 1/T = 25 x (1÷ ½) = 50 cm/sec
31Factors Affecting the Speed of Sound Sound waves require matter to travelNo particles to compress = no waves = no soundSpeed of sound depends on matter or mediumSpeed does not depend of the sourceFactors that affect the speed of sound include:Temperature of mediumElasticity of mediumDensity of medium
32Speed of Sound Temperature Affects Temperature changes affect sound speed more in gases than solids or liquidsParticles spaced apart in gasesTemperature affects spacing of particles in gases (Charles & Boyles Gas Laws)TemperatureHigh temperature air = higher sound speedLow temperature air = lower sound speedHeat and sound = kinetic energy
33Speed of Sound Elasticity Elasticity = The tendency of an object to return to its original shape once the forces are no longer applied.Phases of matter have great effect on elasticity of matterGreater elasticity = Greater speed of soundvsolids > vliquids > vgases
34Speed of Sound Density Less effect on speed of sound than elasticity Within a single phase of matter = greater impactDensity = mass/volumeWithin a single phase of matterGreater density = lower speed of soundMass of heavier particles are harder to moveGreater density = Greater inertia
35Speed of Sound Materials Material Speed of Sound (m/s) Iron 5890 Lead The speed of sound varies through different materialsMaterialSpeed of Sound (m/s)Iron5890Lead1960Water1479Ice3980Air330
36Sonic BoomWhen an object travels faster than the speed of sound it breaks the “sound barrier”Waves all traveling at same speed, pile up on each other as plane pushes them togetherResult is a “sonic boom”
37Properties of Sound Intensity-measure of sound’s amplitude Related to loudness, but loudness is subjectiveIntensity measured in decibels (dB)Increase in 10 dB results in sound that is twice as loudSourceIntensity Level (dB)Threshold of hearing (TOH)Rustling leaves10Whisper20Normal conversation60Busy street traffic70Vacuum cleaner80Rock concert110Threshold of pain130Military jet takeoff140Eardrum perforation160
38Properties of Sound Frequency and Pitch Frequency is number of waves in a certain amount of timeFrequency is measured in Hertz (Hz)Pitch is related to frequency, describes how high or low the sound is. Pitch is subjective.Pitch is the sensation of frequenciesHigh frequency = high pitched soundsLow frequency = low pitched sounds
39Human Hearing and Frequency Humans can hear frequencies ranging from 20-20,000 HzUltrasound are sound waves with frequencies above the human hearing range
40Properties of Sound Sound Quality is referred to Timbre Differences in timbre allow listeners to hear not only the difference between an oboe and a flute, but also the difference between two different flutes, even if both flutes are playing notes at the same frequency and amplitude
41Properties of Sound Descriptions related to timbre Warm Mellow ResonantDark or BrightHeavy or LightFlatHaving much, little, or no vibratoDescriptions related to timbreReedyBrassyClearRoundedPiercingStridentHarsh
42Properties of Sound Doppler Effect The observed effect between an observer and a sound source when one is moving relative to anotherdistance decreasing → perceived frequency (pitch) is increaseddistance increasing → perceived frequency (pitch) is decreased
43Doppler Effect Examples (visual)(visual and audio)
44Wave InteractionsWhat is the result of collisions between waves and other waves or objects?Waves transfer energyCollisions results in energy transferLose or gain energy
45Wave Interactions Wave colliding with other waves cause interference Principle of SuperpositionWaves add (subtract) amplitudes (energy)Two kinds of interferenceConstructive (add)Destructive (subtract)
46Sound Wave Interactions InterferenceConstructive = increase in intensityDestructive = decrease in intensity
47Wave Interactions Constructive Interference waves add to produce a new wave with larger peaks than either of the two original waves
51Phase shifts of wavesThe phase shift tells an observer how out of sync two or more waves areIt gives the offset of the two wavesIn phase = constructive interferenceOut of phase = destructive interference
52In phase and out of phase waves Waves are completely out of phase– destructive interferenceWaves are completely in phase– constructive interference
53Sonic Boom Constructive interference of waves = sonic boom Crack of a bull whip = sonic boom
57HomeworkComplete Sound and Standing Waves Worksheets
58Sound Wave Interactions ResonanceIs the vibration of an object at its natural frequencyThis frequency depends on the length of the object
59Sound Wave Interactions ResonanceTuning forks and bells vibrate at their natural frequencyAll objects have a frequency that they resonate atWhen waves bounce back and forth on themselves within the object and constructively interfere, we call it resonance.
60Sound Wave Interactions Resonance Examples(Movie of Tacoma Narrows Bridge)
61Wave InteractionsWave colliding with objects have following 3 outcomesRefractionReflectionDiffraction
62Wave Interactions REFLECTION Reflection is when waves bounce from a surface back toward the source.A mirror reflects the image of the observer.None of the characteristics of a wave are changed by reflection.No change-wavelength, frequency, periodChange-wave direction
63Wave Interactions REFLECTION Law of Reflection Angle of Incidence = Angle of Reflection
64Sound Wave Interactions ReflectionWhen a sound wave in air reaches the surface of another material, some of the sound is reflected off the surface and some passes into the material (transmitted)
65Sound Wave Interactions ReflectionSmooth surfaces bestmore sound will be reflected from a smooth wall made of mud than a pile of dirtreason is that the rough or porous surface allows for many reflections, resulting in more absorption and less reflection
66Sound Wave Interactions ReflectionsEchoesWhen sound reflects off a smooth flat surface, an echo or reproduction of the sound can be heard.Echoes are more noticeable if the surface is far enough away to allow for a time-lag between when the sound is made and when it is hear. (~0.1 seconds)
67Echo ProblemIf the speed of sound in air is 340 m/sec and you hear an echo 1 sec after you yell, how far away is the reflector?Remember that that the sound wave has to travel there and back soV=total distance/time340m/sec= total distance/1 secTotal distance = 340 m/sec x 1 sec= 340 mDistance to reflector = total distance ÷ 2= 170 m
68Wave Interactions DIFFRACTION Diffraction is the bending of waves when they collide with the edges of objects.All waves diffract.We can hear around a corner because of the diffraction of sound waves.
69Sound Wave Interactions DiffractionBecause sound waves diffract, you can hear around corners and from behind obstacles
70Wave Interactions REFRACTION Refraction is when waves are deflected when passing from one medium to anotherThe wave generally changes direction.
71Sound Wave Interactions Refraction is the bending of waves when they enter a medium where their speed is different.
72Sound Wave Interactions Refraction-EffectCool air-lower speed, Warm air-higher speedNormally, only the direct sound is received. But refraction can add some additional sound, effectively amplifying the sound. Natural amplifiers can occur over cool lakes.