Photo Album

by Robert MacKay

Sound waves are longitudinal waves

• http://faraday.physics.utoronto.ca/IYearLab/Intros/StandingWaves/Flash/tunefork.html

Audible range 20 – 20,000 Hzdecreases with age and damage

Speed of sound in Air

• Depends of the air temperature. Higher air temperture the higher the speed.

• Depends of the molecular mass of air. Faster in helium, slower in air, and slower yet in Xenon.

skm

3

1about

T 0.6 331.5m/s)(in air in sound of speed C

or

• During a lightning storm the thunder is heard 6 seconds after the flash. How far away was the lightning strike?

• During a lightning storm the thunder is heard 6 seconds after the flash. How far away was the lightning strike?

2 km

Speed of sound in Air

• Depends of the air temperature. Higher air temperture the higher the speed.

• Depends of the molecular mass of air. Faster in helium, slower in air, and slower yet in Xenon.

smi

or

51or ft/s 1100about

T 0.6 331.5m/s)(in air in sound of speed C

• During a lightning storm the thunder is heard 10 seconds after the flash. How far away was the lightning strike?

• During a lightning storm the thunder is heard 10 seconds after the flash. How far away was the lightning strike?

2 miles

Speed of sound in solids

• Depends of the elasticity of solid. The stiffer the solid the higher the speed.

• Depends of the solid density. The lower a solid’s density the higher the speed.

Beats

• The beat frequency is the difference between two frequencies.

21 fffBeat

Beats are used in tuning

• when tuning a guitar a beat frequency of 3 Hz is heard when comparing the sound from the guitar to 256 Hz tuning fork.

• What is the guitar string’s frequency?

Beats are used in tuning

• when tuning a guitar a beat frequency of 3 Hz is heard when comparing the sound from the guitar to 256 Hz tuning fork.

• What is the guitar string’s frequency? 253 or 259 Hz (can’t say for sure which one)

Beats are used in tuning

• when tuning a guitar a beat frequency of 3 Hz is heard when comparing the sound from the guitar to 256 Hz tuning fork. The string is then slightly tightened and a beat frequency of 4 Hz is observed.

• What is the guitar string’s frequency now?

Beats are used in tuning

• when tuning a guitar a beat frequency of 3 Hz is heard when comparing the sound from the guitar to 256 Hz tuning fork. The string is then slightly tightened and a beat frequency of 4 Hz is observed.

• What is the guitar string’s frequency now? 260 Hz

Decibel Sound LevelDecibel Sound LevelDecibel Sound LevelDecibel Sound LevelSource of Sound Intensity (W/m^2) Sound Level dBJet at 30 m 1E+02 140

1E+00 120Disco Music 1E-01 110

1E-02 100Riveter 1E-03 90

1E-04 801E-05 70

Busy Street traffic 1E-06 601E-07 50

Quiet Radio 1E-08 401E-09 30

Whisper 1E-10 201E-11 10

Threshold of Hearing 1E-12 0

it’s actually easyit’s actually easyit’s actually easyit’s actually easy• intensity 10 (101) louder 10 dB higher

• intensity 100 (102) louder 20 dB higher

• intensity 1000 (103) louder 30 dB higher

• intensity 10,000 (104) louder 40 dB higher

• intensity 1,000,000 (106) louder 60 dB higher