1. Sound Notes

2. Standing Waves
A standing wave is produced when a wave that is traveling is reflected back upon itself. There are two main parts to a standing wave:
Antinodes – Areas of MAXIMUM AMPLITUDE
Nodes – Areas of ZERO AMPLITUDE.

3. Sound Waves
Sound Waves are a common type of standing wave as they are caused by RESONANCE.
Resonance – when a FORCED vibration matches an object’s natural frequency thus producing vibration, sound, or even damage.
Example - shattering a wine glass by hitting a musical note that is on the same frequency as the natural frequency of the glass.
Example – Tacoma bridge collapse

4. Resonance Example Tacoma Narrows Bridge Collapse
mCGs

5. Electromagnetic vs Mechanical Waves
Electromagnetic wave - capable of transmitting its energy through a vacuum (or empty space).
Produced by the vibration of charged particles.
Ex. All light waves
Mechanical wave - not capable of transmitting its energy through a vacuum.
Require a medium in order to transport their energy from one location to another.
Ex. Sound, slinky, water, standing waves.
Two ways to categorize waves – Transverse vs Longitudinal and Electromagnetic vs Mechanical

6. Sound Waves Longitudinal waves produced by a vibration
Changes in pressure (high to low)
Molecules in the air vibrate about some average position creating the compressions and rarefactions.
a wavelength is the distance from a compression to the next compression (or from a rarefaction to the next rarefaction)

7. Frequency Wavelength of a wave tells you the frequency
Frequency is measured in Hertz (Hz)
Frequency is the pitch of a sound
High pitch = high frequency/ Low pitch = low frequency
Doubling the frequency = octave

8. Frequency High frequencies are high sounds (whistle) with high pitches
Low frequencies are low sounds (tuba) with low pitches.
Who has higher frequencies, women or men?

9. Loudness Amplitude of a wave, tells you the loudness
Measure in decibels (dB)
Increase of 20 dB = twice the volume
Loud
Soft

10. Sound Levels

11. Loudness of Sound in Decibels
Loudness (dbs)
Hearing Damage
Average Home
40-50
Loud Music
90-100
After long exposure
Rock Concert
Progressive
Jet Engine
Pain

12. Human Hearning Below 20 Hz – Infrasonic
Elephants communication,
Average human hearing (audible sound) ranges from 20 Hz to 20,000 Hz
Above 20,000 Hz – Ultrasonic
Ultasounds

13. Sound medium Most sounds are transmitted through air
In general, sounds are transmitted easily in solids, then liquids, and slowest is air (gases.)
Ex. Hold your ear to the ground to hear horses off at a distance.
Speed of Sound in Various Media
Medium
Speed of Sound (m/s)
Air (0°C)
331
Air (20°C)
343
Helium (0°C)
972
Water (25°C)
1493
Seawater (25°C)
1533
Copper (25°C)
3560
Iron (25°C)
5130

14. Sound Wave Interference
Two speakers (green dots) generating sound. Listeners at the red points will hear the sound better than listeners at the blue points.
Why?
Thus, constructive interference occurs wherever a thick line meets a thick line (or thin line meets a thin line) this type of interference results in antinodes (red dots).
Blue dots are the nodes, places of destructive interference.

15. Doppler Effect
phenomenon observed whenever the source of waves is moving with respect to an observer.
observed to occur with all types of waves - water waves, sound waves, and light waves.

16. Doppler Effect
Ex. A police car traveling towards you on the highway. As the police car approached with its siren blasting, the pitch of the siren sound was high; and then suddenly after the car passed by, the pitch of the siren sound was low. 

17. Speed of Sound To calculate the speed of sound, use the equation:
speed = distance/time s = d/t
speed = frequency)(wavelength) v = fλ
Speed depends on the medium.
Will be given a chart of the various speeds in different mediums.

18. Speed of Sound
Sound waves with a constant frequency of 250Hz are traveling through air at 0 C. What is the wavelength of the sound waves?
Speed of Sound in Various Media
Medium
Speed of Sound (m/s)
Air (0°C)
331
Air (20°C)
343
Helium (0°C)
972
Water (25°C)
1493
Seawater (25°C)
1533
Copper (25°C)
3560
Iron (25°C)
5130