Unit 3: Energy On the Move

Transcription

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2 10 Table of Contents Unit 3: Energy On the Move Chapter 10: Waves 10.1: The Nature of Waves 10.2: Wave Properties 10.3: The Behavior of Waves

3 10.1 The Nature of Waves What s in a wave? wave is a repeating disturbance or movement that transfers energy through matter or space. Examples?

4 10.1 The Nature of Waves Waves and Energy Click image to view movie

5 10.1 The Nature of Waves Waves and Energy Because it is moving, the falling pebble has energy. As it splashes into the pool, the pebble transfers some of its energy to nearby water molecules, causing them to move. What you see is energy traveling in the form of a wave on the surface of the water.

6 10.1 The Nature of Waves Waves and Matter Imagine you re in a boat on a lake. Approaching waves bump against your boat, but they don t carry it along with them as they pass.

7 10.1 The Nature of Waves Waves and Matter The waves don t even carry the water along with them. Only the energy carried by the waves moves forward. All waves have this property they carry energy without transporting matter from place to place.

8 10.1 The Nature of Waves Making Waves A wave will travel only as long as it has energy to carry.

9 10.1 The Nature of Waves Making Waves

10 10.1 The Nature of Waves Making Waves It is the up-and-down motion of your hand that creates the wave. Anything that moves up and down or back and forth in a rhythmic way is vibrating. The vibrating movement of your hand at the end of the rope created the wave. In fact, -All waves are produced by something that vibrates.

11 10.1 The Nature of Waves Mechanical Waves Medium- matter the waves travel through is called a The medium can be a solid, a liquid, or gas

12 10.1 The Nature of Waves Mechanical Waves mechanical waves- Waves that can travel only through a medium. Not all waves need a medium. Light and radio waves, can travel through space. (No Medium) The two types of mechanical waves are transverse waves and compressional waves.

13 10.1 The Nature of Waves Transverse Waves transverse wave, Waves move at right angles to the direction that the wave travels. (Like water waves) For example, a water wave travels horizontally as the water moves vertically up and down.

14 10.1 The Nature of Waves Compressional Waves compressional wave, waves move the same direction that the wave travels. You can model compressional waves with a coiled spring toy.

15 10.1 The Nature of Waves Compressional Waves Squeeze several coils together at one end of the spring. Then let go of the coils.

16 10.1 The Nature of Waves Compressional Waves As the wave moves, it looks as if the whole spring is moving toward one end. The wave carries energy, but not matter, forward along the spring. Compressional waves also are called longitudinal waves.

17 10.1 The Nature of Waves Sound Waves Sound waves are compressional waves. When a noise is made, such as when a locker door slams shut and vibrates, nearby air molecules are pushed together by the vibrations.

18 10.1 The Nature of Waves Sound Waves The air molecules are squeezed together like the coils in a coiled spring toy are when you make a compressional wave with it. The compressions travel through the air to make a wave.

19 10.1 The Nature of Waves Sound in Other Materials Sound waves also can travel through other mediums, such as water and wood. When a sound wave reaches your ear, it causes your eardrum to vibrate. Your inner ear then sends signals to your brain, and your brain interprets the signals as sound.

20 10.1 The Nature of Waves Water Waves Ocean waves are formed most often by wind blowing across the ocean surface. The size of the waves that are formed depend on the wind speed, the distance over which the wind blows, and how long the wind blows.

21 10.1 The Nature of Waves Seismic Waves Forces in Earth s crust can cause regions of the crust to shift, bend, or even break. The breaking crust vibrates, creating seismic (SIZE mihk) waves that carry energy outward.

22 10.1 The Nature of Waves Seismic Waves Seismic waves are a combination of compressional and transverse waves. They can travel through Earth and along Earth s surface. The more the crust moves during an earthquake, the more energy is Click image to view movie released.

23 10.1 Section Check Question 1 What is a wave? Answer A wave is a repeating movement that transfers energy through matter or space.

24 10.1 Section Check Question 2 Which is carried by a water wave? A. a boat on the surface B. boat anchor submerged 50 m C. energy D. water molecules

25 10.1 Section Check Answer The answer is C. Waves carry energy without transporting matter from place to place.

26 10.1 Section Check Question 3 Which type of wave does not need a medium? A. electromagnetic B. mechanical C. ocean D. sound

27 10.1 Section Check Answer The answer is A. Electromagnetic waves are made by vibrating electric charges and can travel through space where matter is not present.

28 10.2 Wave Properties The Parts of a Wave Waves can differ in how much energy they carry and in how fast they travel. Waves also have other characteristics that make them different from each other.

29 10.2 Wave Properties The Parts of a Wave crests - Alternating high points troughs - Alternating low points

30 10.2 The Parts of a Wave Parts of a compressional wave Compressionregion where the coils are close together. Wave Properties

31 10.2 Wave Properties The Parts of a Wave Rarefaction- region where coils are spread apart

32 10.2 Wavelength Wave Properties wavelength is the distance between two of the same points on a wave

33 10.2 Wavelength Wave Properties

34 10.2 Wavelength Wave Properties The wavelengths of sound waves that you can hear range from a few centimeters for the highest-pitched sounds to about 15 m for the deepest sounds.

35 10.2 Wave Properties Frequency and Period frequency of a wave is the number of wavelengths that pass a fixed point each second. transverse waves- number of crests that pass by a point each second. Frequency is expressed in hertz (Hz).

36 10.2 Wave Properties Frequency and Period Period- amount of time it takes one wavelength to pass a point.

37 10.2 Wave Properties Wavelength is Related to Frequency As frequency increases, wavelength decreases. If you move the rope up, down, and back up in 1 s, the frequency of the wave you generate is 1 Hz.

38 10.2 Wave Properties Sound and Mediums Sound travel faster in liquids and solids than they do in gases. Light waves travel more slowly in liquid and solids than they do in gases or in empty space. Sound waves faster in a material if the temperature of the material is increased.

39 10.2 Wave Properties Calculating Wave Speed You can calculate the speed of a wave represented by v by multiplying its frequency times its wavelength.

40 10.2 Wave Properties Amplitude and Energy Amplitude energy carried by a wave. The greater the wave s amplitude is, the more energy the wave carries. Click image to play movie

41 10.2 Wave Properties Amplitude of Compressional Waves The closer the coils are in a compression, the farther apart they are in a rarefaction.

42 10.2 Wave Properties Amplitude of Transverse Waves Draw Picture

43 10.2 Section Check Question 1 If a wave has a high point and a low point, is it a compressional or transverse wave?

44 10.2 Section Check Answer Transverse waves have alternating high points, called crests, and low points, called troughs.

45 10.2 Section Check Question 2 What is the wavelength of a wave?

46 10.2 Section Check Answer A wavelength is the distance between one point on a wave and the nearest point just like it.

47 10.2 Section Check Question 3 Which of the following refers to the number of wavelengths that pass a fixed point each second? A. frequency B. period C. wavelength D. wave speed

48 10.2 Section Check Answer The answer is A. Period is a length of time, and wavelength is a distance.

49 Your turn. Section 1 review page Section 2 review page

50 10.3 The Behavior of Waves To Be a Wave All waves must- Reflect, Refract, and Diffract.

51 10.3 Reflection How does the reflection of light allow you to see yourself in the mirror? It happens in two steps. First, light strikes your face and bounces off. Then, the light reflected off your face strikes the mirror and is reflected into your eyes. What about Sound Waves The Behavior of Waves

52 10.3 Echoes The Behavior of Waves Echo - sound waves hit an object, they reflect and come back to you. You hear the sound multiple times.

53 10.3 The Law of Reflection Draw this Picture: The beam striking the mirror is called the incident beam. The beam that bounces off the mirror is called the reflected beam. The Behavior of Waves

54 10.3 The Behavior of Waves The Law of Reflection The line drawn perpendicular to the surface of the mirror is called the normal.

55 The Behavior of Waves 10.3 The Law of Reflection The angle formed by the incident beam and the normal is the angle of incidence. The angle formed by the reflected beam and the normal is the angle of refection.

56 10.3 The Law of Reflection law of reflection- The angle of incidence is equal to the angle of refection. All reflected waves obey this law. The Behavior of Waves

57 10.3 Refraction The Behavior of Waves When a wave passes from one medium to another. It changes speed and direction. (Example: from air to water) If the wave is traveling at an angle when it passes from one medium to another, it changes direction, or bends, as it changes speed.

58 10.3 Refraction The Behavior of Waves Refraction- Bending of a wave caused by a change in its speed as it moves from one medium to another.

59 10.3 The Behavior of Waves Refraction of Light in Water Light waves travel slower in water than in air. This causes light waves to change direction and bend toward the normal When light waves travel from air to water, they slow down and bend toward the normal.

60 10.3 The Behavior of Waves Refraction of Light in Water You may have noticed that objects that are underwater seem closer to the surface than they really are. In the figure, the light waves reflected from the swimmer s foot are refracted away from the normal and enter your eyes.

61 10.3 The Behavior of Waves Refraction of Light in Water However, your brain assumes that all light waves have traveled in a straight line. The light waves that enter your eyes seem to have come from a foot that was higher in the water.

62 10.3 Diffraction The Behavior of Waves When waves strike an object, several things can happen. The waves can bounce off, or be reflected. If the object is transparent, light waves can be refracted as they pass through it. Waves also can behave another way when they strike an object. The waves can bend around the object.

63 10.3 Diffraction The Behavior of Waves Diffraction - an object causes a wave to change direction and bend around it. Diffraction and refraction both cause waves to bend. The difference is that refraction occurs when waves pass through an object, while diffraction occurs when waves pass around an object.

64 10.3 Diffraction The Behavior of Waves After they pass through the opening, the waves spread out.

65 10.3 The Behavior of Waves Diffraction and Wavelength Examples of diffraction?

66 10.3 The Behavior of Waves Hearing Around Corners Light waves have a much shorter wavelength. They are hardly diffracted at all by the door.

67 10.3 The Behavior of Waves Diffraction of Radio Waves AM radio waves have longer wavelengths than FM radio waves do. Because of their longer wavelengths, AM radio waves diffract around obstacles like buildings and mountains. As a result, AM radio reception is often better than FM reception around tall buildings and natural barriers such as hills.

68 10.3 Interference interference When two or more waves overlap and combine to form a new wave The Behavior of Waves

69 The Behavior of Waves 10.3 Constructive Interference constructive interference- waves add together.

70 10.3 The Behavior of Waves Constructive Interference

71 10.3 The Behavior of Waves Destructive Interference destructive interference- waves cancel each other.

72 10.3 The Behavior of Waves Standing Waves standing wave - waves equal in wavelength and amplitude, travel in opposite directions, and interfere with each other.

73 10.3 The Behavior of Waves Standing Waves in Music When the string of a violin is played with a bow, it vibrates and creates standing waves. Some instruments, like flutes, create standing waves in a column of air.

74 10.3 Resonance The Behavior of Waves resonance - object is made to vibrate by absorbing energy at its natural frequency If enough energy is absorbed, the object can vibrate so strongly that it breaks apart.

75 10.3 Section Check Question 1 State the law of reflection. Answer According to the law of reflection, the angle of incidence is equal to the angle of reflection.

76 10.3 Section Check Question 2 is the bending of a wave caused by a change in its speed as it moves from one medium to another. A. diffraction B. diffusion C. refraction D. reflection

77 10.3 Section Check Answer The answer is C. The greater the change in speed is, the more the wave bends.

78 10.3 Section Check Question 3 Which is the means by which you can hear around corners? A. diffraction B. diffusion C. reflection D. refraction

79 10.3 Section Check Answer The answer is A. Diffraction occurs when an object causes a wave to change direction and bend around it.

80 Quiz handout Your turn.

81 11 Table of Contents Unit 3: Energy On the Move Chapter 11: Motion 11.1: The Nature of Sound 11.2: Properties of Sound 11.3: Music 11.4: Using Sound

82 11.1 The Nature of Sound What causes sound? Every sound is produced by an object that vibrates. For example, your friends voices are produced by the vibrations of their vocal cords, and music from a carousel and voices from a loudspeaker are produced by vibrating speakers.

83 11.1 Sound Waves The Nature of Sound Sound waves are compressional waves. A compressional wave is made up of two types of regions called compressions and rarefactions.

84 11.1 Sound Waves The Nature of Sound When a radio speaker vibrates outward, the nearby molecules in the air are pushed together to form compressions.

85 11.1 Sound Waves The Nature of Sound When the speaker moves inward, the nearby molecules in the air have room to spread out, and a rarefaction forms.

86 11.1 Sound Waves The Nature of Sound As long as the speaker continues to vibrate back and forth, compressions and rarefactions are formed.

87 11.1 The Nature of Sound Traveling as a Wave Compressions and rarefactions collide with air molecules as energy is transferred. Compression- Air molecules close together Rarefaction- Air molecules spread apart A series of compressions and rarefactions travel to your ear that we interpret as sound

88 11.1 The Nature of Sound Moving Through Materials Most sounds you hear travel through air to reach your ears. If you ve ever been swimming underwater and heard garbled voices, you know that sound also travels through water.

89 11.1 The Nature of Sound Moving Through Materials Sound waves can travel through any type of matter solid, liquid, or gas. The matter that a wave travels through is called a medium. Sound waves cannot travel through empty space.

90 11.1 The Speed of Sound in Different Materials The Nature of Sound The speed of a sound wave through a medium depends on the substance the medium is made of and whether it is solid, liquid, or gas.

91 11.1 The Speed of Sound in Different Materials The Nature of Sound Sound travels the slowest through gases, faster through liquids, fastest through solids.

92 11.1 The Speed of Sound in Different Materials The denser the material the the closer the molecules are together which makes it easier and faster to transfer sound The Nature of Sound

93 11.1 The Speed of Sound in Different Materials Speed of sound doesn t depend on the loudness. The Nature of Sound All sounds travel through a medium at the same speed.

94 11.1 The Nature of Sound A Model for Transmitting Sound A line of people passing a bucket is a model for molecules transferring the energy of a sound wave.

95 11.1 The Nature of Sound A Model for Transmitting Sound When the people are far away from each other, like the molecules in gas, it takes longer to transfer the bucket of water from person to person.

96 11.1 The Nature of Sound A Model for Transmitting Sound The bucket travels quickly down the line when the people stand close together. The closer the particles, the faster they can transfer energy from particle to particle.

97 11.1 Temperature and the Speed of Sound The Nature of Sound As the temperature of a substance increases, its molecules move faster. Molecules more likely to collide with each other increasing sound speed. Click image to view movie

98 11.1 The Nature of Sound Human Hearing Vocal cords and mouths move in many different ways to produce various kinds of compressional waves. Your ears and brain work together to turn the compressional waves caused by speech, music, and other sources into something that has meaning.

99 11.1 The Nature of Sound Human Hearing 1 st Ear gathers the compressional waves. 2 nd Ear amplifies the waves. 3 rd Waves are converted to nerve impulses that travel to the brain. 4 th Brain decodes and interprets the nerve impulses.

100 11.1 The Nature of Sound Gathering Sound Waves The Outer Ear

101 11.1 Gathering Sound Waves The Outer Ear The Nature of Sound Outer ear, Middle ear, and Inner ear. The outer ear is where sound waves are gathered.

102 11.1 Gathering Sound Waves The Outer Ear The Nature of Sound The eardrum is a tough membrane about 0.1 mm thick. When incoming sound waves vibrate the eardrum

103 11.1 cochlea The Nature of Sound Converting Sound Waves The Inner Ear filled with liquid and contains tiny hair cells. Converts sound to nerve impulses

104 11.1 Section Check Question 1 What type of wave is a sound wave? Answer A sound wave is a compressional wave.

105 11.1 Section Check Question 2 In which of the following environments would sound waves not travel? A. at altitudes of 10,000 15,000 m B. in solid aluminum C. on the Moon D. under water

106 11.1 Section Check Answer The answer is C. Sound waves require a medium through which to travel. So, sound waves cannot travel through empty space.

107 11.1 Section Check Question 3 Which region of the ear amplifies sound waves? A. ear drum B. inner ear C. middle ear D. outer ear

108 11.1 Section Check Answer The answer is C. The bones of the middle ear amplify sound waves.

109 11.2 Properties of Sounds Intensity and Loudness What happens to the sound waves from your radio when you adjust the volume? The notes sound the same as when the volume was higher, but something about the sound changes.

110 11.2 Properties of Sounds Intensity and Loudness The difference is that quieter sound waves do not carry as much energy as louder sound waves do.

111 11.2 Properties of Sounds Intensity and Loudness The amount of energy a wave carries corresponds to its amplitude. For a compressional wave, amplitude is related to the density of the particles in the compressions and rarefactions.

112 11.2 Properties of Sounds Intensity and Loudness strongly vibrating objects makes sound waves with tight, dense compressions. Weak vibrations make sound waves with less dense compressions.

113 11.2 Properties of Sounds Intensity and Loudness The density of particles in the rarefactions behaves in the opposite way. It is important to remember that matter is not transported during the compression and rarefaction of a compression wave only energy is transported. Matter compresses and expands as the wave of energy passes through the matter.

114 Properties of Sounds 11.2 Intensity Intensity- amount of energy that flows through a certain area.

115 11.2 Intensity Properties of Sounds Volume Increases = Intensity Increases Volume decreases = Intensity decreases

116 11.2 Intensity Properties of Sounds Intensity = how far away sound can be heard. If you and a friend whisper a conversation, the sound waves you create have low intensity and do not travel far.

117 11.2 Properties of Sounds Intensity Decreases with Distance Intensity influences how far a wave will travel because some of a wave s energy is converted to other forms of energy when it is passed from particle to particle. low intensity = less distance sound travels. High intensity = farther distance sound travels

118 11.2 Loudness Properties of Sounds Loudness is the human perception of sound intensity. When sound waves of high intensity reach your ear, they cause your eardrum to move back and forth a greater distance than sound waves of low intensity do.

119 11.2 Loudness Properties of Sounds The bones of the middle ear convert the increased movement of the eardrum into increased movement of the hair cells in the inner ear. As a result, you hear a loud sound

120 11.2 Properties of Sounds A Scale for Loudness Sound intensity is measured in decibels (db)

121 11.2 Properties of Sounds A Scale for Loudness

122 11.2 Pitch Properties of Sounds If you were to sing a scale, your voice would start low and become higher with each note. Pitch- how high or low a sound seems to be. pitch is related to the frequency of the sound waves.

123 11.2 Properties of Sounds Frequency and Pitch High Pitch = High Frequency Low Pitch = Low frequency

124 11.2 Properties of Sounds Frequency and Pitch This figure shows different notes and their frequencies. A healthy human ear can hear sound waves with frequencies from about 20 Hz to 20,000 Hz.

125 11.2 Properties of Sounds Ultrasonic and Infrasonic Waves ultrasonic - waves above 20,000 Hz, High pitched waves humans cannot hear

126 11.2 Properties of Sounds Ultrasonic and Infrasonic Waves Ultrasonic waves are used in medical diagnosis and treatment. They also are used to estimate the size, shape, and depth of underwater objects.

127 11.2 Properties of Sounds Ultrasonic and Infrasonic Waves Infrasonic waves frequencies below 20 Hz too low for most people to hear.

128 11.2 Properties of Sounds Ultrasonic and Infrasonic Waves These waves are produced by sources that vibrate slowly, such as wind, heavy machinery, and earthquakes.

129 11.2 Properties of Sounds The Doppler Effect Doppler effect- change in pitch or wave frequency due to a moving wave source

130 11.2 Moving Sound Properties of Sounds As a race car moves, it sends out sound waves in the form of compressions and rarefactions. The race car creates a compression, labeled A. Compression A moves through the air toward the flagger standing at the finish line.

131 11.2 Moving Sound Properties of Sounds By the time compression B leaves the race car, the car has moved forward. Because the car has moved since the time it created compression A, compressions A and B are closer together than they would be if the car had stayed still.

132 11.2 Moving Sound Properties of Sounds As a result, the flagger hears a higher pitch.

133 11.2 Properties of Sounds A Moving Observer The Doppler effect happens any time the source of a sound is changing position compared with the observer. It occurs no matter whether it is the sound source or the observer that is moving. The faster the change in position, the greater the change in frequency and pitch.

134 11.2 Properties of Sounds Using the Doppler Effect Radar guns use the Doppler effect to measure the speed of cars. Weather radar also uses the Doppler shift to show the movement of winds in storms, such as a tornado.

135 11.2 Section Check Question 1 Each unit on the scale for sound intensity is called a.

136 11.2 Section Check Answer The answer is decibel, abbreviated db.

137 11.2 Section Check Question 2 Sound frequencies above 20,000 Hz are called waves. A. infrasonic B. infrared C. subsonic D. ultrasonic

138 11.2 Section Check Answer The answer is D. Subsonic and infrasonic are waves with frequencies below 20 Hz.

139 11.2 Section Check Question 3 Describe the Doppler effect.

140 11.2 Section Check Answer The Doppler effect is the change in pitch due to a moving wave source. effect.

141 11.4 Accoustics Using Sound When an orchestra stops playing, does it seem as if the sound of its music lingers for a couple of seconds? reverberation The echoing effect produced by many reflections of sound During an orchestra performance, reverberation can ruin the sound of the music.

142 11.4 Accoustics Using Sound Acoustics- study of sound Some scientists and engineers specialize in acoustics to make concert halls and other theaters pleasant EXAMPLES!!

143 11.4 Accoustics Using Sound They know that soft, porous materials can reduce excess reverberation, so they might recommend that the walls of concert halls be lined with carpets and draperies.

144 11.4 Echolocation Using Sound At night, bats swoop around in darkness without bumping into anything. Their senses of sight and smell help them navigate. Echolocation is the process of locating objects by emitting sounds and interpreting the sound waves that are reflected back.

145 11.4 Sonar Sonar system that uses the reflection of underwater sound waves to detect objects. Using Sound

146 11.4 Using Sound Ultrasound in Medicine One of the important uses of ultrasonic waves is in medicine. Using special instruments, medical professionals can send ultrasonic waves into a specific part of a patient s

147 11.4 Using Sound Ultrasound in Medicine Reflected ultrasonic waves are used to detect and monitor conditions such as pregnancy, certain types of heart disease, and cancer.

148 11.4 Using Sound Ultrasound Imaging Like X rays, ultrasound can be used to produce images of internal structures. The sound waves reflect off the targeted organs or tissues, and the reflected waves are used to produce electrical signals. A computer program converts these electrical signals into video images, called sonograms.

149 Using Sound 11.4 Treating with Ultrasound Sometimes small, hard deposits of calcium compounds or other minerals form in the kidneys, making kidney stones. Ultrasonic treatments are commonly used to break them up.

150 11.4 Using Sound Treating with Ultrasound Bursts of ultrasound create vibrations that cause the stones to break into small pieces. These fragments then pass out of the body with the urine.

151 11.4 Section Check Question 1 The process of locating objects by emitting sounds and interpreting the sound waves that are reflected back is A. called acoustics. B. echolocation C. infrasonic tracking D. reverberation

152 11.4 Section Check Answer The answer is B. Echolocation is used by some animals such as bats and dolphins.

153 11.4 Section Check Question 2 Which of the following is not a use of ultrasonic technology in medicine? A. examination of the gallbladder B. examination of bones C. fetal monitoring in utero D. kidney stone treatment

154 11.4 Section Check Answer The answer is B. Ultrasound is not as useful as X rays for examining bones, because hard tissues absorb ultrasonic waves instead of reflecting them.

155 11.4 Section Check Question 3 What is sonar? Answer Sonar is a system that uses the reflection of underwater sound waves to detect objects.