1. Chapter 21: Sound

3. What is sound?
Sound is a form of energy produced by the vibration of matter.
Sound is a compressional or longitudinal wave
Ex. Spring
The particles of the substance vibrate back and forth along the path that the sound wave travels

4. Sound is transmitted through solids, liquids, and gases (air).
What is sound?
Sound is transmitted through solids, liquids, and gases (air).
But the air does not travel with the sound

5. Less dense; not as many particles to interfere.
Sound is transmitted better through solids and liquids. Why?
More dense
Gases transmits sound a lot farther than a solid and liquid. Why?
Less dense; not as many particles to interfere.

6. The greater the elasticity, the greater the speed.
So what causes sounds to travel better through some substances and not others?
The greater the elasticity, the greater the speed.
The greater the density, the slower the speed.
The best conductors of sound are elastic substances.

7. Sound needs a medium in order for it to be transmitted.
Sound can not be transmitted through a vacuum.
Sound needs a medium in order for it to be transmitted.
Radio waves can travel through a vacuum; no medium is needed.
This is why astronauts can use radio signals to talk in space.

8. Speed of Sound 344 m/s in air at 20°C Depends on: Type of medium
travels better through liquids and solids
can’t travel through a vacuum
Temperature of medium
travels faster at higher temps

9. Your ears change sound waves into electrical signals
How you detect sound
Your ears change sound waves into electrical signals
Outer ear: pinna (collects sound waves and directs them into the ear canal)

10. Ear drum: tympanum (Vibrates the ear drum)
How you detect sound
Middle Ear: increases the size of the vibrations (hammer, anvil, stirrup-3 bones)
Ear drum: tympanum (Vibrates the ear drum)
Inner Ear: vibrations created by sound are changed into electrical signals for the brain to interpret (cochlea)

11. Properties of Sound
Speed of sound is affected by the medium it travels through
Temperature affects sound
The cooler the medium the slower the sound travels
The warmer the medium the faster the sound travels

12. Properties of Sound Pitch highness or lowness of a sound
depends on frequency of sound wave
human range: ,000 Hz
High frequency = high pitch
Low frequency = low pitch
ultrasonic waves
subsonic waves

13. Frequencies you cannot hear
Ultrasonic: higher than 20,000 Hz
Uses: clean jewelry, medical applications
Infrasonic: lower than 20 Hz
Found: in the atmosphere and in the crust when plates move; also an indication motion sickness

14. Human Hearing Intensity
Volume, or loudness, of sound: the measure of how well a sound can be heard
depends on energy (amplitude) of sound wave
measured in decibels (dB)
Above 120 dB can cause hearing loss.

15. Human Hearing
DECIBEL SCALE
120
110
100 80 70 40 18 10

16. Doppler Effect moving toward you - pitch sounds higher
change in wave frequency caused by a moving wave source or when the observer of the sound moves
moving toward you - pitch sounds higher
moving away from you - pitch sounds lower

17. Seeing with Sound Sound waves are invisible
A device known as an oscilloscope graphs representations of sound waves

18. Seeing with Sound Ultrasonic waves - above 20,000 Hz Medical Imaging
SONAR
“Sound Navigation and Ranging”

19. Reflection of Sound Waves
Echoes are reflected sound waves
The strength of the reflection depends on the reflecting surface
Are best reflected off smooth hard surfaces
Echolocation: process using reflected sound waves to find objects
Bats
Whales
SONAR
Ultrasonography

20. Interference Interference
the ability of 2 or more waves to combine to form a new wave
Constructive - louder
Destructive - softer

21. Interference
Beats
variations in sound intensity produced by 2 slightly different frequencies
both constructive and destructive interference occur

22. Cool Interference Examples:
The Sound Barrier: the point at which the source of a sound accelerates to the speed of sound
Sonic Booms: the explosive sound heard when a shock wave reaches your ears
1st time sound barrier broken: Oct. 14, 1947 by Chuck Yeager (speed of sound is called Mach 1); so Mach 6 is going 6 times the speed of sound

23. Chuck Yeager Breaks the Sound Barrier

24. Sound Barrier and Sonic Booms

25. Resonance Forced Vibration
when one vibrating object forces another object to vibrate at the same frequency
results in a louder sound because a greater surface area is vibrating
used in guitars, pianos, etc.

26. Resonance Resonance special case of forced vibration
object is induced to vibrate at its natural frequency

27. Harmonics Fundamental Overtones
the lowest natural frequency of an object
Overtones
multiples of the fundamental frequency

28. Music vs. Noise Music Noise specific pitches and sound quality
regular pattern
Noise
no definite pitch
no set pattern
Any sound that is a random mix of frequencies or pitches

29. Acoustics Acoustics Reverberation the study of sound
echo effect produced by the reflection of sound
Anechoic chamber - designed to eliminate reverberation.