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

2. 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

3. 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

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

5. 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.

6. 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.

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

8. 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

9. 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.

10. 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.

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

12. 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.

13. 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.

14. 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.

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