3 What types of waves can you identify in a wave pool @ at amusement park? In a wave pool, energy is being carried across the pool in the form of waves.The sounds of laughter and talking in the pool are also being carried by waves.
4 Mechanical WavesMechanical wave- a disturbance in matter that carries energy from one place to anotherYou can see the effects of a wave’s energy in the wave pool when it lifts people in the water. Mechanical waves require matter to travel through.
5 Medium Medium- material through which a wave travels solids, liquids, and gases can all act as mediumsWaves travel through a rope when you shake one end of it. Rope = medium
6 How are mechanical waves created? Vibration- a repeating back-and-forth motionA mechanical wave is created when a source of energy causes a vibration to travel through a medium.
7 3 Types of Mechanical Waves There are three (3) main types of mechanical waves:TransverseLongitudinalSurface
8 Transverse WavesTransverse wave- wave that causes the medium to vibrate at right angles to the direction in which the wave travelsThese waves carry energy from left to right in a direction perpendicular to the up and down motion of the mediumExample: shaking one end of a rope up and down
9 Parts of a Transverse Wave Crest- the highest point of the wave above the rest positionTrough- the lowest below the rest position
10 Parts of a Transverse Wave Identify points B, D, F, & H as either crests or troughs.
11 QUESTIONHow does the direction of a transverse wave compare with the direction of the medium? Answer: They are opposite/perpendicular!
12 Longitudinal WavesLongitudinal wave- wave in which the vibration of the medium is parallel to the direction the wave travelsExample: SoundWave in spring moving BACK and FORTH (not up and down)P-Waves - longitudinal waves produced by earthquakes
13 Parts of a Longitudinal Wave Compression- the area where the particles in a medium are spaced close togetherRarefaction- the area where the particles in a medium are spread out
14 Parts of a Longitudinal Wave Label at least one compression and one rarefaction on the longitudinal wave below:CompressionRarefaction
15 QuestionHow does the direction of a longitudinal wave compare with the direction of the medium? Answer: They are the same/parallel!
16 Surface WavesSurface wave- wave that travels along a surface separating two mediaExample- ocean wavesThey occur at the surface between water and airA bobber floating in the waves will travel in a circle because the motion from these surface waves is both up-and-down and back-and-forth like in the transverse and longitudinal wavesMost waves do not move matter from one place to another
17 Most waves do not move matter from one place to another…however When the waves approach the shore they behave differentlyWhat causes a wave to break?As a wave enters shallow water the bottom of the wave has too much friction acting on it from the seafloor, while the top of the wave continues at its original speedAs a result, the wave carries the medium and anything in it toward the shore
20 Surfing Question: How do surfers know when the next wave is coming? Answer: They can count the time between crests, and the next crest will usually follow this pattern. They can do this because waves follow periodic motion.
21 Periodic MotionPeriodic motion- any motion that repeats at regular time intervalsMany things display periodic motion
22 The surfers were timing the PERIOD Period- time required for one cycle, a complete motion that returns to its starting pointFor an ocean wave, the period is the time between 2 successive crests
23 FrequencyTo find how many crests pass in a given time, you need to know the frequency Frequency- number of complete cycles in a given timeThe frequency of a wave is how many wave cycles pass a point in a given timeFrequency is measured in cycles per second, or hertz (Hz)A wave’s frequency equals the frequency of the vibrating source producing the wave
25 WavelengthWavelength- distance between a point on one wave and the same point on the next cycle of the waves.For a transverse wave, the wavelength is measured between adjacent crests or between adjacent troughsFor longitudinal waves, the wavelength is the distance between the center of a compression to the center of the next compression
27 Wavelength & Frequency Question: When wavelengths are shorter, the crests are closer together, is the frequency higher or lower? Answer: HIGHER! Increasing the frequency of a wave decreases its wavelength!
28 Which has the highest frequency? _______ Which has the lowest frequency? _______ Which has the shortest wavelength? _______ Which has the longest wavelength? _______AB
29 Wave SpeedTo determine how fast a wave is traveling, remember how we find speed: distance/timeIn waves, distance is like wavelength, and time is period. So we can solve for the speed of a wave using the following formula: Speed = WAVELENGTH x FREQUENCY
30 Solving for Wave SpeedThe units for wave speed are the same as the units for speed we covered earlier:meters per second (m/s)If we keep speed constant, wavelength is inversely proportional to frequencyWhat does this mean if you have 2 waves with different frequencies?The wave with the lower frequency has a longer wavelengthRefer to Math Skills on page 506 for practice
31 Amplitude…Energy…Consider the difference in the waves you would see if you dropped a pebble into the water compared to a cannonball…. Which waves would be higher?The cannonball
32 Amplitude & EnergyAmplitude- the maximum displacement of the medium from its rest positionConsidered the “height” of the waveThe more energy a wave has, the greater its amplitude
33 What do you think of when you hear the word reflection? 17.3: Behavior of WavesWhat do you think of when you hear the word reflection?Now…relate that thought to waves!!!
34 Wave ReflectionReflection- occurs when a wave bounces off a surface that it cannot pass through, ex: echoThe reflection of a wave is like the reflection of a ball thrown at a wall. The ball cannot go through the wall so it bounces back. If you send a transverse wave down a rope attached to a wall, the wave reflects when it hits the wall
36 Wave ReflectionReflection does not change the speed or frequency of a wave, but the wave can be flipped upside down. If the reflection occurs at a fixed boundary (wall), then the reflected wave will be upside-down compared to the original wave (see picture on previous slide)
37 Wave RefractionRefraction- the bending of a wave as it enters a new medium at an angleAs an ocean wave approaches the shore at an angle, the wave bends, or refracts toward shore because one side of each wave front hits before the other side does as it gets into shallow water. Refraction of the wave occurs only when the two sides of a wave travel at different speeds.
38 Wave RefractionWhen a wave enters a medium at an angle, refraction occurs because one side of the wave moves more slowly than the other side.
39 Wave DiffractionDiffraction- the bending of a wave as it moves around an obstacle or passes through a narrow opening.The pattern is very similar to the circular ripples you see when a pebble is tossed into a pond. A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle
40 Examples of Wave Diffraction A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle
41 Wave DiffractionThe pattern is very similar to the circular ripples you see when a pebble is tossed into a pond.
42 InterferenceInterference occurs when two or more waves overlap and combine togetherThere are two types of interference:constructive interferencedestructive interference
44 Constructive Interference Constructive interference- occurs when two or more waves combine to produce a wave with a larger displacement (taller), ex: crest meets crest
45 Destructive Interference Destructive interference- occurs when two or more waves combine to produce a wave with a smaller displacement, ex: crest meets trough
46 Standing WavesStanding waves- wave that appears to stay in one place – it does not seem to move through the mediumInterference from reflected waveYou can observe one if you pluck a guitarOnly certain points are stationary- called nodes.
48 Sound Waves QUESTION: What type of waves are sound waves? Hint: compressions and rarefactions travel through a medium in sound waves ANSWER: Longitudinal Waves
49 Sound WavesHere's what sound waves look like. The caption reads, "A visible pattern of sound waves. This new technique of studying sound demonstrates the focusing effect of an acoustical lens on sound waves issuing from the horn at extreme left.
50 Properties of Sound Some properties of sound: Speed Intensity Loudness FrequencyPitch
51 Speed of a WaveIt takes time for sound to traveltravels at 342 m/s
52 Speed of Sound Varies…Refer to Figure 14 on page 514 for the speeds of sound in different media!Generally, sound waves travel fastest in solids, slower in liquids, and slowest in gasesThis is partly due to the spacing of the particles in each phase
53 IntensityIntensity- rate at which a wave’s energy flows through a given areaSound intensity depends on both wave’s amplitude and the distance from the sound sourceMeasured in decibel (dB)See Figure 15: Sound Intensity LevelWhisper: dBRock Concert: dBJet Plane (taking off): dB
54 Intensity depends on wave’s amplitude (energy) and distance from the sound source If someone whispers in your ear, the sound intensity may be greater than when someone shouts at you from the other end of a field
55 LoudnessLoudness- physical response to the intensity of sound, modified by physical factorsSubjective, open to interpretation As intensity increases, loudness increases, however:Loudness also depends on factors such as the health of your ears and how your brain interprets the information in sound waves!
56 Frequency of a Sound Wave Vibration becomes faster as sound frequency becomes higherThe frequency of a sound wave depends on how fast the source of the sound is vibratingIn musical instruments, the size of the tubing through which air moves produces different frequenciesLonger tubing = longer wavelength = lower frequency
57 Pitch of a Sound Wave frequency of a sound as you perceive it High-frequency sounds have a high pitchLow-frequency sounds have a low pitchBUT pitch, like loudness, depends on other factors such as your age and health of your ears!
58 Ultrasound Most people hear sounds between 20 Hz and 20,000 Hz. Infrasound: sound at frequencies lower than most people hearUltrasound: sound at frequencies higher than most people hearUltrasound is used in a variety of applications, sonar & ultrasound imaging
59 SonarSonar: a technique for determining the distance to an object under waterStands for SOund NAvigation and RangingDistance calculated by using the speed of sound in water and the time that the sound wave takes to reach and object and the echo takes to return
61 Doppler EffectDoppler Effect - a change in sound frequency caused by motion of the sound source, motion of the listener, or bothAs a source of sound approaches, an observer hears a higher frequencyWhen the sound source moves away, the observer hears a lower frequencyThis is due to the sound waves being close together and spread out
63 Hearing & the EarYou are able to pick up slight vibrations in the air from sound because your ear has a membrane that vibrates when a sound wave strikes it.The outer ear gathers, and focuses sound into the middle ear like a funnelThe middle ear receives and amplifies the vibrationsThe inner ear uses nerve endings to sense vibrations and send signals to the brain to decode
65 Recording SoundSound is recorded by converting sound waves into electronic signals that can be processed and storedSound is reproduced by converting electronic signals back into sound wavesLarger-diameter speakers are better at reproducing lower frequencies of sound (like a bass drum)Smaller-diameter speakers are better for reproducing higher frequencies of sound (like a small bongo drum)
67 MusicMost instruments vary pitch by changing the frequency of standing wavesResonance- the response of a standing wave to another wave of the same frequencyThink of a child being pushed on a swing…if the pushes are timed at the right frequency, the child can swing higher and higher.In the same way, one wave can “push” another wave to a higher amplitude