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Waves and Sound. Intro A. Pick up your notes and worksheet packets B. Write the following questions on a blank piece of paper (don’t answer yet) 1. What.

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Presentation on theme: "Waves and Sound. Intro A. Pick up your notes and worksheet packets B. Write the following questions on a blank piece of paper (don’t answer yet) 1. What."— Presentation transcript:

1 Waves and Sound

2 Intro A. Pick up your notes and worksheet packets B. Write the following questions on a blank piece of paper (don’t answer yet) 1. What is the difference between a mechanical and electromagnetic wave? 2. What is the difference between a transverse and longitudinal wave? 3. What do all waves transfer? 4. What don’t waves transfer?

3 Section 1: Intro to Waves

4 Waves –Are disturbances that move through an empty space or through medium (material) –Waves transfer energy without transferring matter. –Particles of medium move in simple harmonic motion Mechanical: Through a medium Electromagnetic: Through empty space

5 Mechanical wave: –Caused by a disturbed medium and move by action reaction of particles –ex: water wave, sound A medium is matter particles like gas (ex. air), liquid (ex. Water), and solid (ex. earth) Two types of mechanical waves that require a medium Transverse Wave Longitudinal Wave

6 Electromagnetic wave: Move through empty space (no medium) Created by moving electrons Ex. radio waves, microwaves, light SOL= 3.0 x 10 8 m/s Through empty space Types Electromagnetic Waves

7 In order to start and transmit a wave, a source of disturbance (vibration) and a disturbed medium are required. Mechanical caused by vibrating particles –Like seen here Electromagnetic by vibrating electrons

8 Damping: A decrease in the amplitude of a wave Caused by energy loss or the spreading out of the wave over a larger area.

9 Wave pulse is a single wave disturbance Wave train (continuous wave) - is a series of pulses at intervals

10 Section 2: Types of Mechanical Waves Transverse Longitudinal

11 Transverse Wave: Wave particles move perpendicular to the direction the wave travels Ex. vibrating string of a musical instrument Perpendicular to the direction of travel Direction of travel

12 Parts of a transverse wave Crest Trough Equilibrium Position Wavelength (ג) amplitude

13 Crest- highest point on a transverse wave Trough- lowest point on a transverse wave Equilibrium position- center around which simple harmonic motion occurs Amplitude- from the equilibrium position to the crest or trough

14 Longitudinal Wave: Particles vibrate parallel to the direction the wave travels ex. sound wave Direction of travel Particles vibrate parallel to the direction of travel

15 Parts of a Longitudinal Wave: Compression- point where the particles are closest together Rarefaction- point where the particles are furthest apart Compression Rarefaction

16 Intro Questions 1.What do all waves transfer? 2.What don’t waves transfer? 3.What starts a wave? Pick between the following choices and answer this correctly: 4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.

17 Section 3: Relationship between Wavelength, Frequency and Wave Speed

18 velocity ( v ): speed of the wave. –unit: m/s (meter/second) frequency ( f ): vibrations per second of the wave –unit: Hz (hertz) wavelength ( ג ): length of one wave pulse –unit: m (meter)

19 Lets revisit our old equation What is the velocity of an object that moves 25 meters in 3 seconds? V= ___ dtdt

20 Lets revisit our old equation What is the velocity of an object that moves 25 meters in 3 seconds? V= ___ dtdt

21 Now lets look at the new equation you can use as well. V= ___ dtdt oldnew Example what is the velocity of a wave that has a frequency of 3Hz and a wavelength of 5m?

22 Now lets look at the new equation you can use as well V= ___ dtdt oldnew

23 Now lets look at the new equation you can use as well V= ___ dtdt oldnew

24 Now lets look at the new equation you can use as well V= ___ dtdt oldnew

25 Now lets look at the new equation you can use as well V= ___ dtdt oldnew

26 Relationship between frequency and wavelength. Wavelength and frequency are inversely related As frequency goes up the wavelength gets shorter (assuming no change in velocity) Click for animation

27 Period (T) vs. Frequency (f) Period (T) – seconds for one cycle –(unit s) Frequency (f) – cycles for one second –(unit Hz) If you know one you can solve for the other

28 Example 1 Wave Math The frequency of a wave is 560 Hz. What is its period?

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30 Example 2 Wave Math A girl floats in the ocean and watches 12 wave crests pass her in 46 s. Calculate the wave: a) frequencyb) period

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32 Example 3 Wave Math The period of a wave is 0.044s. How many cycles will the energy source make in 22s? cycles second

33 The period of a wave is 0.044s. How many cycles will the energy source make in 22s?

34 Example 4 Wave Math A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude? 0.33m 0.24m

35 Example 4 Wave Math A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude? 0.33m 0.66m

36 Example 4 Wave Math A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude? 0.24m 0.12m

37 Example 5 Wave Math What is the speed of a 256 Hz sound with a wavelength of 1.35 m?

38 Example 5 Wave Math What is the speed of a 256 Hz sound with a wavelength of 1.35 m?

39 Example 6 Wave Math You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m. A. What is the frequency? B. What is the period? C. What is the velocity?

40 Example 6 Wave Math You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m. A. what is the frequency B. What is the period C. Velocity

41 Assignment to work on: CP Worksheet Packet Section 3 Honors Worksheet Packet Section 3 Book Problems 4,5,6 pg

42 Pendulum Lab day: Your into is to read over your lab; I will ask you if there are any questions soon Equilibrium Position Amplitude (A) Length (L)

43 Pendulum Lab day One complete cycle

44

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46 Intro after pendulum lab All labs are due today: Turn them in on my desk 1.Your pendulum makes 5 complete cycles in 10 seconds. a.What is the pendulums frequency? b.What is the pendulums period? 2.What is the definition of frequency (can be in equation form) 3.When you increase the length of the pendulum string, what happens to frequency?

47 Section 4: The Pendulum

48 Pendulum- a weight on a string that moves in simple harmonic motion (swings back and forth). Movement from a to c and back to a is one complete cycle or vibration accelerating decelerating This is the equilibrium position.

49 Simple harmonic motion- vibration about an equilibrium position –Constant back and forth motion over the same path. –15º is the maximum angle for a pendulum to have simple harmonic motion where our equations work

50 Masses do not effect the period in simple harmonic motion. What effects the period: L – length of the string g – acceleration due to gravity

51 Click here to interact with a pendulum

52 Example 7 A tall tree sways back and forth in the breeze with a frequency of 2Hz. What is the period of this tree?

53 Example 7 A tall tree sways back and forth in the breeze with a frequency of 2Hz. What is the period of this tree?

54 Hypnotist Paulbar the great swings his watch from a 0.20 m chain in front of a subjects eyes. What is the period of swing of the watch. Example 8

55 Hypnotist Paulbar the great swings his watch from a 0.20 m chain in front of a subjects eyes. What is the period of swing of the watch. Example 8

56 A spider swings slightly in the breeze from a silk thread that is 0.09 m in length. What is the period of the simple harmonic motion? Example 9

57 A spider swings slightly in the breeze from a silk thread that is 0.09 m in length. What is the period of the simple harmonic motion? Example 9

58 If a pendulum is shortened, does the period increase or decrease? What about its frequency? Example 10

59 If a pendulum is shortened, does the period increase or decrease? What about its frequency? Example 10 Period decreases Frequency increases

60 Finish section 4 of the worksheets and turn in your packet today when you are done. Work on something else quietly while you wait for everyone to complete their work

61 Section 5: Wave Interactions Reflection Refraction Diffraction Interference

62 Reflection: The turning back of a wave at the boundary of a new medium Ex: light off a mirror, or sound echo Incident wave- incoming

63 Waves reflected off a fixed boundary are inverted. –A fixed boundary is one not allowed to move

64 Waves reflected off a flexible boundary are upright. –A flexible boundary is allowed to move

65 Law of Reflection: Angle of reflection of a wave equals angle of incidence θ r = θ i Normal line – line perpendicular to surface being reflected off of. θrθr θiθi Normal line

66 Example 11 Draw the reflected wave, labeling angles of incidence, reflection, and the normal line 35º

67 Wave front: Portion of a medium’s surface in which particles are in phase Particles in phase are in the same stage of their vibration.

68 Which two of these particles would be in phase? Example 12

69 Refraction: the bending of a wave path as it enters a new medium obliquely (indirectly) caused by difference in speed of the new medium fast to slow – bends toward the normal line slow to fast – bends away from normal

70 Refraction Light travels slower in water

71 Normal Line θiθi θrθr slow Fast medium

72 Example 13 Draw the refracted wave, labeling the normal line, angle of incidence, and angle of refraction. Slow Fast

73 Draw the refracted wave, labeling the normal line, angle of incidence, and angle of refraction. Slow Fast θiθi θrθr Normal line Example 13

74 Diffraction: Spreading of waves around edges or through an opening of a boundary Is greatest when size of opening is smaller than wavelength

75 Principle of Superposition: Displacement of a medium by two or more waves is the algebraic sum of the displacements of the waves alone

76 Interference: Result of the superposition of two or more waves constructive- (crest meets crest or trough meets trough) amplitudes add destructive – (crest meets trough) amplitudes subtract Only temporary as paths cross

77 Constructive interference Only temporary as paths cross

78 Destructive interference Only temporary as paths cross

79 Constructive and destructive interference in two sine waves

80 Example 14 (finish off the drawings) BeforeDuringAfter Constructive interference Destructive interference

81 Antinodal line Lines of constructive interference Nodal line Lines of destructive interference Wave Fronts Interfering

82 Standing wave: created by waves with same frequency, wavelength, and amplitude traveling in opposite directions and interfering. consists of nodes (o amplitude) and antinodes (max amplitude) produced by certain frequencies

83 Standing Waves Being Produced NodeAntinode

84 Show what you know 1. Refraction happens when waves – a)Turn back at a boundary b)Enter a new medium at an angle. c)Go through an opening. d)Are superpositioned.

85 2. This diagram shows which wave interaction? a)Reflection b)Refraction c)Diffraction d)Interference

86 3. Constructive interference occurs when- a)Crest meets crest b)Trough meets trough c)Amplitudes add up d)All of these

87 4. A line along which the medium does not vibrate is called a a)Nodal line b)Antinodal line c)Construction

88 5. Standing waves are produced by waves of equal ________ traveling in opposite directions. a)Wavelength b)Frequency c)Amplitude d)All of the above

89 Intro Questions 1.An echo bouncing off a nearby wall tends to ________________ back toward the source. 2.A pendulum requires 3 seconds to make one back and forth motion. Calculate the pendulum’s frequency? 3. Steam is rising from a cup of hot tea. What type of thermal energy transfer is occurring? (conduction, convection, or radiation) 4. What type of interference would occur when these waves meet? 5. A water wave has a speed of 5m/s and the distance between each crest is 2.0m. What is the frequency of the water wave?

90 Section 6: Sound

91 Sound waves are produced by a vibrating object Sound waves are longitudinal mechanical waves.

92 Sound Frequency: Determines pitch 20 – 20,000 Hz are audible to an average person Less than 20 Hz are infrasonic Greater than 20,000 Hz are ultrasonic

93 Uses of ultrasonic waves

94 More than 20,000 Hz- Ultrasonic waves

95 Echolocation and Sonar Sonar is simply making use of an echo. An echo is used to locate an object. When an animal or machine makes a noise, it sends sound waves into the environment around it. Those waves bounce off nearby objects, and some of them reflect back to the object that made the noise. Whales, Dolphins, Bats, and many more organisms use sound for locating prey and predators

96 Less than 20 Hz- Subsonic or Infrasonic Sound

97 Sound Velocity Largely depends on medium elasticity Solids>liquids>gasses Then depends on temperature –Faster at higher temperatures –Air (at 0ºC) v = 331 m/s and +/- 0.6 m/s per ºC Generally between phases v solids > v liquids > v gases

98 Sound Velocity Equations v = T c v = d/t v = fλ

99 Interesting sound facts Sound travels 15 times faster in the steel from a railroad track. Sound travels 4 times faster in water At sea level, the speed of sound is 340 m/s or 760 mi/hr. This is called mach 1.

100 The speed of sound will be the same for all frequencies under the same conditions. –Wavelength and frequency are inversely related –As frequency goes up the wavelength gets shorter

101 What is the speed of sound at room temperature (22ºC) Example 15

102 What is the speed of sound at room temperature (22ºC)

103 How many seconds will it take to hear an echo if you yell toward a mountain 110 m away on a day when air temperature is ºC? Example 16

104 How many seconds will it take to hear an echo if you yell toward a mountain 110 m away on a day when air temperature is -6.0 ºC?

105 Example 17 If sound travels at 340 m/s, how many seconds will it take thunder to travel 1609m?

106 Example 17 If sound travels at 340 m/s, how many seconds will it take thunder to travel 1609m?

107 Example 18 A sonar echo takes 3.1s to go to a submarine and back to the ship. If sound travels at 1400m/s in water, how far away is the submarine?

108 Example 18 A sonar echo takes 3.1s to go to a submarine and back to the ship. If sound travels at 1400m/s in water, how far away is the submarine?

109 Example 19 On a day when air temperature is 11ºC, you use a whistle to call your dog. If the wavelength of the sound produced is 0.015m, what is the frequency? Could you hear the whistle?

110 Example 19 On a day when air temperature is 11ºC, you use a whistle to call your dog. If the wavelength of the sound produced is 0.015m, what is the frequency? Could you hear the whistle?

111 Intro 1. A 25,000Hz dog whistle can be heard by a dog but not by humans because the frequency is in the ______________ range. 2. An elephant can hear below 20 Hz. This is the _________ range. 3. The range we can hear is between _____ and _______ and we call this range ______________. 4. Which of the following will sound travel fastest in? a) a swimming pool b) a steel bridge c) a vacuum d) warm air 5. Sound wave A has twice the frequency of sound wave B. That means that sound wave A must _______________ a) travel faster than sound wave B b) have a shorter wavelength than sound wave B c) have a lower pitch that sound wave B d) be louder than sound wave B

112 Section 7: The Doppler Effect

113 Doppler Effect Change in pitch caused by relative motion of source and observer Pitch increases as sound and observer approach (and vice versa)

114 Doppler Effect Example u/jw/doppler.htm#examplehttp://www.animations.physics.unsw.edu.a u/jw/doppler.htm#example

115 Examples/Uses Doppler radar: detects storm fronts and their approach speed.

116 Radar Gun

117 Doppler Effect Problems Frequency rises when its coming closer and lowers when moving away.

118 Example 20 Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies towards her at a speed of m/s? (use 340 m/s as the speed of sound)

119 Example 20 Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies towards her at a speed of m/s? (use 340 m/s as the speed of sound)

120 Example 21 Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies away from her at a speed of m/s? (use 340 m/s as the speed of sound)

121 Example 21 Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies away from her at a speed of m/s? (use 340 m/s as the speed of sound)

122 Example 22 A sparrow chases a crow with a speed of 4.0 m/s, while chirping at a frequency of Hz. What frequency of sound does the crow hear as he flies away from the sparrow at a speed of 3.0 m/s? (use 340 m/s as the speed of sound)

123 Example 22 A sparrow chases a crow with a speed of 4.0 m/s, while chirping at a frequency of Hz. What frequency of sound does the crow hear as he flies away from the sparrow at a speed of 3.0 m/s? (use 340 m/s as the speed of sound)

124 Intro You are chasing after your parent’s car because you forgot your lunch in it. You are running at a swift 4.0 m/s and your parent is going 12 m/s. It is a cold 5.0° C today and your voice is producing a frequency of 460 Hz. Your parent’s car is squealing a bit and producing a frequency of 760 Hz. 1.What frequency would your parent hear you at if he/she could? 2.What frequency do you hear your parent’s car at?

125 You are chasing after your parent’s car because you forgot your lunch in it. You are running at a swift 4.0 m/s and your parent is going 12 m/s. It is a cold 5.0° C today and your voice is producing a frequency of 460 Hz. Your parent’s car is squealing a bit and producing a frequency of 760 Hz. 1.What frequency would your parent hear you at if he/she could?

126 You are chasing after your parent’s car because you forgot your lunch in it. You are running at a swift 4.0 m/s and your parent is going 12 m/s. It is a cold 5.0° C today and your voice is producing a frequency of 460 Hz. Your parent’s car is squealing a bit and producing a frequency of 760 Hz. 2. What frequency do you hear your parent’s car at?

127 Section 8: Intensity and Perceived Sound

128 The property of sound waves associated with loudness is amplitude The property associated with pitch is frequency

129 Sound Intensity is the rate of transferring energy through an area

130 The Decibel Scale Threshold of hearing (I o )- –the minimum intensity sound that can be heard at certain frequencies I o = 1.0 x ß = 0 dB at the threshold of hearing

131 More on the Decibel Scale The decibel scale relates sound intensity to human hearing –An intensity of 0 dB is when there is enough energy for an average human to detect the sound –1-dB in intensity level is the smallest change in loudness that an average listener can detect –If the relative intensity level increases by 10 dB, the new sound seems approximately twice as loud as the original sound.

132 Section 9: Resonance and Music

133 Resonance in Music Forced Vibration- The vibration of an object that is made to vibrate by another vibrating object. Sympathetic vibrations- secondary vibrations caused by forced vibration of a first object. Sounding board- part of an instrument forced into vibration to amplify sound

134 Example of creating forced vibrations to make a sound louder Sounding board of a musical instrument. Example: guitar makes a strings vibrations resonate

135 Resonance: Also called sympathetic vibrations Dramatic increase in the amplitude of a wave when the frequency of an applied force matches the natural frequency of the object.

136 Resonance can be dangerous Wind caused the Tacoma Narrows suspension bridge to vibrate at its natural frequency. The amplitude of the vibrations caused too much strain on the bridge until it collapsed.

137 Difference between music and noise Noise- a random mixture of a large number of sound frequencies Music- Sound frequency or mixture of frequencies with a pattern

138 Percussion Instrument: Musical sound produced by striking the object Frequency depends on the mass of the object. To raise the pitch- decrease the mass of the object. Ex- drums, xylophone, bells

139 Stringed Instrument Musical sound produced by plucking or blowing strings Frequency depends on four factors To raise pitch –1. decrease diameter of string –2. increase tension –3 decrease length –4. decrease density of string material Examples: guitar, violin

140 Wind Instrument Musical sound produced by vibrating air column Frequency depends mainly on length of air column To raise pitch- decrease the size of the air column Examples- oboe, flute

141 Standing Waves are formed in the instrument due to vibrations When the natural frequency is hit the sound amplifies

142 Open Ended Wind Column Instrument Must be nodes at both ends

143 Closed Ended Wind Column Instrument There is an antinode at the closed end. Count standing waves by including the return trip.

144 Acoustics- field of study related to sound Acoustic designers try to maximize the quality of sound reaching the audience –Control the size, shape, and material used –They try and control the reflection

145 Reverberation- If a reflected sound wave reaches the ear within 0.1 seconds of the initial sound, then it seems to the person that the sound is prolonged. Echoes- A perceived second sound that arrives after the first has died out. –Echoes occur when a reflected sound wave reaches the ear more than 0.1 seconds after the original sound wave was heard. Two types of reflection with sound

146 Interference causes beats –Beats occur due to constructive and destructive interference between sounds with close but not exact frequencies.


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