1. Sound and Wave Interference

2. Sound Waves
Sound is a compressional wave which travels through the air through a series of compressions and rarefactions.

3. Sound travels through different media.
Sound travels different speeds in different media. Sound typically travels faster in a solid that a liquid and faster in a liquid than a gas.
The denser the medium, the faster sound will travel.
The higher the temperature, the faster the particles of the medium will move and the faster the particles will carry the sound.

4. What is sound intensity?
Sound intensity is the energy that the sound wave possesses. The greater the intensity of sound the farther the sound will travel and the louder the sound will appear.
Loudness is very closely related to intensity. Loudness is the human perception of the sound intensity. The unit for loudness is decibels.

5. Loudness in Decibels

6. How is frequency related to pitch?
The pitch of a sound wave is directly related to frequency. A high-pitched sound has a high frequency (a screaming girl). A low-pitched sound has a low frequency (a fog-horn).
A healthy human ear can hear frequencies in the range of 20 Hz to 20,000 Hz. Humans cannot hear below 20 Hz. Sounds below this frequency are termed infrasonic.
Sounds above 20,000 Hz are termed ultrasonic. Some animals, such as dogs, can hear frequencies in this range in which humans cannot hear.

7. Different sounds that you hear include
(A) noise, (B) pure tones, and (C) musical notes.

8. All Shapes of Waveforms
Different Instruments have different waveforms
a: glockenspiel
b: soft piano
c: loud piano
d: trumpet
Our ears are sensitive to the detailed shape of waveforms!
More waveforms:
e: french horn
f: clarinet
g: violin

9. The ear assesses frequency content
The exact mixture of frequency content is how we distinguish voices from one another
effectively, everyone has their own waveform
and corresponding spectrum
though an “A” may sound vastly similar, we’re sensitive to very subtle variations

10. Wave Interference When two wave pass each other their superposition
causes reinforcement or cancellation.

11. Interference

12. Constructive interference
Reinforcement when the crest of one wave overlaps the crest of another
Their individual effects adds together, resulting in a wave increased in amplitude

13. Destructive Interference
Cancellation when crest of one wave overlaps trough of another reducing their individual effects.

14. Sound Wave Interference
Interference occurs when two sounds of different frequencies
are heard superposed.
Constructive interference causes louder sound and destructive
inference cause fainter sound.
This alternating pattern produces a beat.
A piano tuner listens for beats to disappear.

15. Water Wave Interference
Left side is theoretical drawing of an interference pattern.
Right side is the actual interference pattern.

16. Standing Waves
Occurs when a wave reflects upon itself and interferes with itself, making it appear to be still.
Nodes remain stationary Anti nodes-occur half way between nodes

17. Standing Waves
Change the frequency in a standing wave and more nodes/antinodes appear in the event

18. DOPPLER EFFECT
Refers to the change in frequency when there is relative motion between an observer of waves and the source of the waves
Doppler with Sound
Doppler with Water

19. The Doppler effect- Stationary bug Bug swimming
Blue Shift-increase in frequency Red Shift- Decrease in frequency

20. Doppler Shift Gives Radial Velocity
True Velocity
Tangential Velocity
Radar
Radial Velocity

22. Bow waves
V-shaped pattern made by overlapping crest

23. Shock Waves
Produced by supersonic aircraft, three-dimensional cone shaped
Sonic boom – sharp crack heard when conical shell of compressed air that sweeps behind a supersonic aircraft reaches listeners on the ground below.

24. Supersonic

25. Subsonic
- slower than the speed of sound
Supersonic
- faster than the speed of sound
speed of object
Mach Number =
speed of sound