Presentation on theme: "Chapter 21 – The Nature of Sound"— Presentation transcript:
1 Chapter 21 – The Nature of Sound Section 3 – Interactions of Sound Wavespp
2 TERMS TO LEARNReflection – the bouncing back of a wave after it hits a barrierEcho – reflection of sound wavesEcholocation – the process of using reflected sound waves to find objectsInterference – the result of two or more waves overlapping
3 TERMS TO LEARNSonic boom – the explosive sound heard when a shock wave reaches your earsStanding wave – a result of interference in which parts of the wave are at resting position and the other parts have a large amplitude
4 TERMS TO LEARNResonance – this occurs when an object vibrating at or near the resonant frequency of a second object causes the second object to vibrateDiffraction – the bending of waves around barriers or through openings
5 REFLECTIONThe amount a sound waves reflects depends on the reflecting surface.Sound waves reflect best off smooth, hard surfaces.
6 ECHOLOCATIONBats, dolphins, whales and some birds use this technique to hunt for food and/or for navigation.
7 TYPES OF ECHOLOCATION Sonar Stands for sound navigation and ranging Ultrasonic waves are sent down into water. The time it takes for the echo to return helps fishermen determine the location of fish.
8 TYPES OF ECHOLOCATION Ultrasonography Uses echoes to “see” inside a patient’s body without using surgery
9 INTERFERENCE OF SOUND WAVES Happens when two or more waves interactCan be constructive or destructiveConstructive – when waves combine, add the amplitudes togetherDestructive – when sound waves combine, subtract the smaller amplitude from the larger amplitude. “Dead spots” in an auditorium are a result of destructive interference
10 THE SOUND BARRIERAs the source of a sound (such as a jet plane) accelerates to the speed of sound, the sound waves in front of the jet plane compress closer and closer together.
11 SHOCK WAVES AND SONIC BOOMS When a jet travels at supersonic speeds, the sound waves it creates spread out behind it in a cone shape.On the edge of the cone, the sound waves combine by constructive interference to produce a shock wave.
12 SONIC BOOMYou hear a sonic boom when the shock wave reaches you, NOT when the jet breaks the sound barrier
13 RESONANT FREQUENCYThe frequencies at which standing waves are made is called the resonant frequency.Resonant frequencies are sometimes called by special names.The lowest resonant frequency is called the fundamental.
14 OVERTONESHigher resonant frequencies are called overtones. The first overtone is twice the frequency of the fundamental.The second overtone is three times the fundamentalThe third overtone is four times the fundamental.
15 DIFFRACTIONDiffraction is the bending of waves around barriers or through openings.The amount of diffraction depends on the size of the opening, wavelength and frequency of the wave.The greatest diffraction occurs when the size of the barrier is the same size or smaller than the wavelength of the sound wave.
16 DIFFRACTIONHigh frequency sound waves have short wavelengths and do not diffract muchLow frequency sound waves have long wavelengths and diffract a lot.
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