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Chapter 21 – The Nature of Sound Section 3 – Interactions of Sound Waves pp. 612 - 617.

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Presentation on theme: "Chapter 21 – The Nature of Sound Section 3 – Interactions of Sound Waves pp. 612 - 617."— Presentation transcript:

1 Chapter 21 – The Nature of Sound Section 3 – Interactions of Sound Waves pp

2 TERMS TO LEARN Reflection – the bouncing back of a wave after it hits a barrier Reflection – the bouncing back of a wave after it hits a barrier Echo – reflection of sound waves Echo – reflection of sound waves Echolocation – the process of using reflected sound waves to find objects Echolocation – the process of using reflected sound waves to find objects Interference – the result of two or more waves overlapping Interference – the result of two or more waves overlapping

3 TERMS TO LEARN Sonic boom – the explosive sound heard when a shock wave reaches your ears Sonic boom – the explosive sound heard when a shock wave reaches your ears Standing wave – a result of interference in which parts of the wave are at resting position and the other parts have a large amplitude Standing 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 LEARN Resonance – this occurs when an object vibrating at or near the resonant frequency of a second object causes the second object to vibrate Resonance – this occurs when an object vibrating at or near the resonant frequency of a second object causes the second object to vibrate Diffraction – the bending of waves around barriers or through openings Diffraction – the bending of waves around barriers or through openings

5 REFLECTION The amount a sound waves reflects depends on the reflecting surface. The amount a sound waves reflects depends on the reflecting surface. Sound waves reflect best off smooth, hard surfaces. Sound waves reflect best off smooth, hard surfaces.

6 ECHOLOCATION Bats, dolphins, whales and some birds use this technique to hunt for food and/or for navigation. Bats, dolphins, whales and some birds use this technique to hunt for food and/or for navigation.

7 TYPES OF ECHOLOCATION Sonar 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 Ultrasonography –Uses echoes to “see” inside a patient’s body without using surgery

9 INTERFERENCE OF SOUND WAVES Happens when two or more waves interact Happens when two or more waves interact Can be constructive or destructive Can be constructive or destructive –Constructive – when waves combine, add the amplitudes together –Destructive – 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 BARRIER As 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. As 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. 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. On the edge of the cone, the sound waves combine by constructive interference to produce a shock wave.

12 SONIC BOOM You hear a sonic boom when the shock wave reaches you, NOT when the jet breaks the sound barrier You hear a sonic boom when the shock wave reaches you, NOT when the jet breaks the sound barrier

13 RESONANT FREQUENCY The frequencies at which standing waves are made is called the resonant frequency. The frequencies at which standing waves are made is called the resonant frequency. Resonant frequencies are sometimes called by special names. Resonant frequencies are sometimes called by special names. –The lowest resonant frequency is called the fundamental.

14 OVERTONES –Higher resonant frequencies are called overtones. The first overtone is twice the frequency of the fundamental. –The second overtone is three times the fundamental –The third overtone is four times the fundamental.

15 DIFFRACTION Diffraction is the bending of waves around barriers or through openings. Diffraction 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 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. The greatest diffraction occurs when the size of the barrier is the same size or smaller than the wavelength of the sound wave.

16 DIFFRACTION High frequency sound waves have short wavelengths and do not diffract much High frequency sound waves have short wavelengths and do not diffract much Low frequency sound waves have long wavelengths and diffract a lot. Low frequency sound waves have long wavelengths and diffract a lot.


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