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

TERMS TO LEARN 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

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 Diffraction – the bending of waves around barriers or through openings

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

Echolocation The process of using reflected sound waves to find objects. Bats, dolphins, whales and some birds use this technique to hunt for food and/or for navigation.

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.

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

INTERFERENCE OF SOUND WAVES Happens when two or more waves interact 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

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.

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.

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

RESONANT FREQUENCY The 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.

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.

DIFFRACTION 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 greatest diffraction occurs when the size of the barrier is the same size or smaller than the wavelength of the sound wave.

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