1. Sound & Interference

2. 4/4 BR: COPY ALL on to Guided Notes: Characteristics of “Sound” Review
Compressional / Longitudinal wave
Mechanical wave/Transverse
v = 330 m/s in air at 0°C and 340 m/s at 20°C
As tempmedium ↑, velocity ↑
As densitymedium ↑ , velocity ↑
v = f *λ
As frequency ↑, wavelength (λ) ↓
Frequency and pitch are related
Amplitude and “loudness” (decibels) are related

3. Frequency & Resonance

4. Human Hearing Range
The teacher will make a range of sounds. Record whether you can hear each frequency below. 1) 2) 3) 4) 5)
100 Hz
440 Hz
2,000 Hz
12,000 Hz
15,000 Hz

5. Human Hearing Range
Human range is about 20-20,000 Hz
Older people and teens who listen to their music too loud tend to lose the high and low parts of their ranges
A flute’s range is Hz (low B) to Hz (high F).
Ultrasonic: sounds greater than 20,000 Hz
Infrasonic: sounds less than 20 Hz

6. Frequency Human hearing ~ 20 – 20,000 Hz
“ULTRAsound” = “higher than we can hear” (anything above 20,000 Hz).

7. Doppler Effect - Demo Time!!!
Doppler Effect: the apparent change in pitch (frequency) due to position
Listen:
Draw:
Sketch the sound waves as the source is…
Standing still
Moving at Mach 0.7
Moving at Mach 1
Moving at Mach 1.4 (Supersonic)

8. Doppler Effect - Demo Time!!!
Pitch: the frequency of the sound wave
High frequency waves = ________ pitch
Low frequency waves = _________ pitch
Intensity: the loudness, or amplitude of the sound
How does the pitch perceived by the listener change as the siren approaches and then passes the listener?
Does the actual pitch of the siren change as it passes by?
High
Low
No, the actual pitch does not change.
Intensity and apparent high pitch increases as siren approaches.
Intensity and apparent low pitch decreases as siren leaves.

9. Sonic Boom
Sonic Boom
Occurs when the object creating a sound moves faster than the sound waves it creates
Compressions constructively interfere
Ted
The Sound:

10. A Sonic Boom Credit: Ensign John Gay, USS Constellation, US Navy

11. Resonance
Natural frequency – the frequency at which an object wants to vibrate
Resonance – when properly timed small impulses add up to make a much larger amplitude
Ex: wine glass, breaking a glass with a voice

12. Frequency – Disaster!
When structures resonate, results can be disastrous
Tacoma Narrows bridge collapse – 1940
“Galloping Gertie”
Video Clip (full-length)

13. Doppler Effect

14. How Does Radar Work

19. B-2 Spirit Stealth Bomber. Photo by Bobbi Garcia
B-2 Spirit Stealth Bomber. Photo by Bobbi Garcia. Posted here with permission of the AFFTC.

20. F/A 9-Lives ……. super sonic kitty

21. Doppler Formula Observer speed Source speed Perceived frequency Wave
Source speed
Perceived frequency
Wave
speed
Actual frequency
+ if approaching
- if receding

22. No one move!

23. Observer moves
+ if approaching
- if receding

24. Source moves
+ if approaching
- if receding

25. Interference & Beats

26. Demo Time!!! Hoot Tube Singing Rod One end is open Both ends are open
finger

27. Open at both ends:
Open at only one end:

28. Beats – let’s listen!
Beats
Ruben’s Board
Ruben’s Tube

30. Interference & Beats Beats
Created by constructive & destructive interference
Periods of loud sounds followed by soft sounds
Two waves of different frequencies interfere with each other

31. Interference & Beats Beat Frequency
Determined by the difference between the two frequencies
300 Hz sound wave and 302 Hz sound wave will produce 2 beats per second – “Beat Frequency” is 2 Hz

32. Constants
Based on your knowledge how sound travels in different media, rank the following from transmitting sound fastest to slowest:
___Water ___Air ___Solid
Speed of sound at 0°C: 330 m/s
Speed of sound at 22°C: 343 m/s
Example: Calculate the speed of sound in air at -15°C.