1. ~ Nature of Sound ~ 1. What is sound? 2. Human Hearing
3. Properties of Sound
4. Interactions of Sound
5. Sound Quality

2. I. WHAT IS SOUND?

3. I. WHAT IS SOUND?
A Sound wave is a LONGITUDINAL WAVE caused by vibrations of particles back and forth through a medium.
Sound waves are mechanical waves and NEED A MEDIUM TO TRAVEL
Sound waves travel in all directions from the source

4. II. Human Hearing

5. converted to nerve impulses in cochlea
II.Human Hearing
sound wave
vibrates ear drum
amplified by bones
converted to nerve impulses in cochlea

7. III. Properties of Sound

8. A. SPEED OF SOUND 345 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

10. B. PITCH Pitch highness or lowness of a sound
depends on frequency of sound wave
human range: ,000 Hz
ultrasonic waves
subsonic waves

11. C. LOUDNESS Loudness volume of sound
depends on energy (amplitude) of sound wave
measured in decibels (dB)

12. Loudness measured in Decibels
DECIBEL SCALE
120
110
100 80 70 40 18 10

13. D. DOPPLER EFFECT
Have you ever noticed how the sound of a police car siren changes as it moves past you? The changes in pitch you hear are due to a phenomenon known as the Doppler effect. Look at the illustration of the police car to answer these questions.
The police car has passed the woman standing on the sidewalk, but has not yet passed the man. Which observer hears the siren at a higher pitch—the woman or the man?

14. D.DOPPLER EFFECT moving toward you - pitch sounds higher
change in wavelength due to the motion of the source. As the source moves, the waves become bunched up and the pitch (frequency) of the sound changes.
moving toward you - pitch sounds higher
moving away from you - pitch sounds lower

15. Doppler Effect

16. Doppler Effect

17. IV. INTERACTIONS OF SOUND
Reflection
Interference
Resonance

18. A. REFLECTIONS OF SOUND WAVES
Reflections of sound waves are called echos!
Sound waves reflect best off smooth, hard surfaces
ECHOLOCATION
USE OF REFLECTED SOUND WAVES TO FIND OBJECTS

19. Ultrasonic waves are used to see with sound using reflection!
Ultrasonic waves - above 20,000 Hz
SONAR
“Sound Navigation Ranging”
Medical Imaging

20. B. Interference Interference When 2 or more waves overlap
Constructive - louder
Destructive - softer

21. SONIC BOOM
When a jet plane reaches the speed of sound, the sound waves in front of the jet combine by constructive interference. The result is a high density compression (high amplitude) compression called the sound barrier.

24. WATCH THESE VIDEOS!

25. C. 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. The Tacoma Narrows Bridge Disaster
= Resonance =
“Galloping Gertie”
The Tacoma Narrows Bridge Disaster
Wind through a narrow waterway caused the bridge to vibrate until it reached its natural frequency.

28. = Resonance =
Beats
variations in sound intensity produced by 2 slightly different frequencies
both constructive and destructive interference occur

29. V. Sound Quality

30. A. Music vs. Noise Music Noise specific pitches and sound quality
regular pattern
Noise
no definite pitch
no set pattern

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