1. 1. WHAT IS SOUND?

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

3. 1. 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. 2. Human Hearing

5. Human Hearing sound wave Outer Ear: vibrates ear drum
Middle Ear: amplified by bones
Inner Ear: converted to nerve impulses in cochlea

6. 3. Properties of Sound

7. A. 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

8. B. PITCH Pitch highness or lowness of a sound
depends on frequency of sound wave
High pitch=high frequency
Low pitch=low frequency
ultrasonic waves
subsonic waves

9. 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?

10. 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

11. Doppler Effect http://www.fearofphysics.com/Sound/doppler.html

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

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

14. 4. INTERACTIONS OF SOUND
Reflection
Interference
Resonance

15. 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

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

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

19. WATCH THESE VIDEOS!

20. Sonic Boom Sounds from Moving Sources.
A moving source of sound or a moving observer experiences an apparent shift of frequency called the Doppler Effect.
If the source is moving as fast or faster than the speed of sound, the sound waves pile up into a shock wave called a sonic boom.
A sonic boom sounds very much like the pressure wave from an explosion

21. 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.

22. ~ Music vs. Noise ` Music Noise specific pitches and sound quality
regular pattern
Noise
no definite pitch
no set pattern