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# Wave Notes Identify a cycle of harmonic motionIdentify a cycle of harmonic motion Relate pitch of a sound to its frequency and speedRelate pitch of a.

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Wave Notes Identify a cycle of harmonic motionIdentify a cycle of harmonic motion Relate pitch of a sound to its frequency and speedRelate pitch of a sound to its frequency and speed Describe what happens to air when sound moves throughDescribe what happens to air when sound moves through Describe factors that affect the speed of soundDescribe factors that affect the speed of sound Explain the Doppler EffectExplain the Doppler Effect Give examples of forced vibrationsGive examples of forced vibrations Describe the conditions for resonanceDescribe the conditions for resonance Identify the different kinds of electromagnetic wavesIdentify the different kinds of electromagnetic waves Describe & Identify the four types of wave interactionsDescribe & Identify the four types of wave interactions Explain constructive & destructive interferenceExplain constructive & destructive interference

Chapter 13 Waves & Sound

Harmonic Motion Harmonic motion – motion that repeats Occurs in cycles – a unit of motion that repeats over and overOccurs in cycles – a unit of motion that repeats over and over

Harmonic Motion Oscillation – motion that repeats regularly A system with harmonic motion is referred to as an oscillator.A system with harmonic motion is referred to as an oscillator.

Waves Wave a disturbance or vibration that transfers energy through matter or space.a disturbance or vibration that transfers energy through matter or space. OR an oscillation that travels!OR an oscillation that travels! Ex: light, sound, earthquake, ocean wave…

SOUND & LIGHT Waves Both vibrations/oscillationsBoth vibrations/oscillations Sound- waves require a medium (solid,liquid,gas) in which to travel. NO Medium = NO sound Light – Waves can pass through many materials. Doesn’t require a medium Can travel through space. PURE Energy! (electromagnetic waves)

Tidbits about light… Produced by vibrating electrons in atoms.Produced by vibrating electrons in atoms. Carries energy and powerCarries energy and power Intensity is analogous to amplitude & describes energy per second carried by a light wave.Intensity is analogous to amplitude & describes energy per second carried by a light wave. c (speed of light) 3 x 10 8 m/sc (speed of light) 3 x 10 8 m/s

Electromagnetic Spectrum Oscillations of electric particles or magnets create electromagnetic waves (light).Oscillations of electric particles or magnets create electromagnetic waves (light). Range of all frequencies of electromagnetic waves is referred to as the spectrum.Range of all frequencies of electromagnetic waves is referred to as the spectrum.

Electromagnetic Spectrum (see handout)

Wave Interactions Reflection – wave bounces and goes in a new direction.Reflection – wave bounces and goes in a new direction. Refraction – the wave bends as it passes into and through the object.Refraction – the wave bends as it passes into and through the object. Diffraction – The wave bends around an object or through holes in the object.Diffraction – The wave bends around an object or through holes in the object. Absorption – The wave is absorbed and disappears.Absorption – The wave is absorbed and disappears.

The Law of Reflection Incident angle = i Reflected angle = r Law: When a wave is reflected, The angle of incidence (i) = the angle of reflection (r).

Refraction

Index of Refraction Light travels differently through different mediums (s, l, g)Light travels differently through different mediums (s, l, g) If light travels through one medium into another it bends, or refractsIf light travels through one medium into another it bends, or refracts Index of Refraction – describes a materials ability to bend light.Index of Refraction – describes a materials ability to bend light.

Index of Refraction Varies slightly for a material depending on color of light.Varies slightly for a material depending on color of light. Glass/Prism will refract white light, separating it into a rainbowGlass/Prism will refract white light, separating it into a rainbow Water has similar propertiesWater has similar properties

Refraction of Light Continuously absorbed & re- emitted by atoms.Continuously absorbed & re- emitted by atoms. Moves at c between atoms only!Moves at c between atoms only! Frequency does not change, but wavelength does.Frequency does not change, but wavelength does. Change in wavelength is proportional to how speed changes.Change in wavelength is proportional to how speed changes.

Diffraction Light will diffract...Light will diffract... –Shine a flashlight on a wall through a slot in a piece of paper. –As you decrease the size of the slot the light on the wall seems to “spread out”. –The diffraction occurs because the size of the slot is not much wider than the wavelength of the wave.

Sound Waves Waves can only travel through solids, liquids, and gases.Waves can only travel through solids, liquids, and gases. Fastest to slowest : solid, liquid, gas Close molecular connection = faster transmission NO SOUND IN A VACUUM (outer space): NO MATTER for vibrations to travel.

Pitch- how low or high a sound seems Freq & pitch directly related Freq: 20-20,000 Hz  pitch =  freq.  pitch =  freq Infrasonic < 20 Hz ultrasonic > 20,000 Hz Dogs -hear ultrasonic frequencies. Elephants – hear infrasonic freq.

Sound Waves Simulation

Loudness – how intense a sound is Measured in DecibelsMeasured in Decibels Determined by amplitude (amount of energy)Determined by amplitude (amount of energy) Most sounds fall between 0-100 dB.Most sounds fall between 0-100 dB. 0 dB quietest sound & 110 dB front row at a rock concert0 dB quietest sound & 110 dB front row at a rock concert Acoustics- Study of soundAcoustics- Study of sound

Speed of Sound Depends on wind, humidity,temp. 0° C = 330 m/s 20 ° C = 340 m/s Warmer = faster!Warmer = faster! HUMID = FASTERHUMID = FASTER

Sound waves travel slower than light waves What is the approximate distance of a thunderstorm when you note a 3 s delay between the flash of lightning & sound of thunder? (about 20 ° C ) (340m/s ) (3)= 1020m

Speed of Sound Subsonic – speed slower than that of sound.Subsonic – speed slower than that of sound. Supersonic – speed faster than that of sound.Supersonic – speed faster than that of sound. Supersonic jets “squish” sound waves that are created as travels through the air… forming a shock wave cone and a sonic boomSupersonic jets “squish” sound waves that are created as travels through the air… forming a shock wave cone and a sonic boom

Sonic boom

13.10 The Doppler Effect The change in frequency of wave motion resulting from motion of the sender or receiver. Sender or receiver is moving! EX: Siren on police car As approaches-high pitch As moves away- low pitch

Sound Wave Interactions Sound waves canSound waves can –Reflect (hard surfaces) –Refract (through materials) –Diffract (through small openings) –Be absorbed (carpet & soft mats) Reverberations - multiple reflections of sound & can become “garbled”.Reverberations - multiple reflections of sound & can become “garbled”.

13.7 Forced Vibrations & natural frequency An object forced to vibrate due to contact w/ a wave from another vibrating object. Ex: tuning fork

Natural frequency- the frequency at which the least amount of energy is required to produce vibrations. all objects have a natural frequency or set of frequencies at which they vibrate when struck.all objects have a natural frequency or set of frequencies at which they vibrate when struck. Depends on : Elasticity & shape of objectDepends on : Elasticity & shape of object

Tacoma Bridge http://fragg.me/video/tacoma- bridgehttp://fragg.me/video/tacoma- bridgehttp://fragg.me/video/tacoma- bridgehttp://fragg.me/video/tacoma- bridge

13.8 Resonance Resounding or “sounding again”. Result of forced vibrations in an object when the applied frequency matches the natural frequency of the objectResult of forced vibrations in an object when the applied frequency matches the natural frequency of the object EX: tuning forks

13.9 Interference – when 2 waves overlap 2 types 1.Constructive interference- waves add together. Crests and troughs fall at same places. New wave has grater amplitudeNew wave has grater amplitude See P. 222

Destructive interference- Crest of one wave overlaps w/ trough of another. Individual effects reduced. See P. 222 Figure 13.20

Beats- Periodic loudness in sound due to wave interference.

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