Sound. DEF: A pressure variation that is transmitted through matter. Collisions are high pressure / compressions.

Transcription

1 Sound

2 Sound DEF: A pressure variation that is transmitted through matter. Link to pic of bell animation Collisions are high pressure / compressions. Pulls are low pressure / rarefacation. Have same properties as waves in general Reflection (Echo) Interference (Beats, noise canceling)

3 Sound Speed Dependent Upon: Medium traveling through. (Ear on train tracks) Temperature of medium Pressure of medium. Sound will not propagate in a vacuum (no pressure) Accepted Speed of sound at STP (Standard Temp. and Pressure) 20 degrees Celcius (68 deg F) and 1 Atm of pressure (14.69 psi) VSound = 343 m/s (1125 ft/s)

4 Speed of sound in various Media Media Temperature (C) Speed (m/s) Air Air Water Salt Water Rubber Iron

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6 You are at home and you see lightning followed by a clap of thunder. They are 15 seconds apart. How far away is the storm?

7 Loudness Loudness is amplitude of sound wave. Human ear is fearfully and wonderfully made. Can detect a change in pressure of 1 billionth of an Atm. (Why your ears pop driving, flying, and swimming) Hearing occurs over a huge spectrum of pressures: a logarithmic scale is used. Decibels (db) Sound level measuring scale.

8 The Ear How Stuff Works How Hearing Works Ear Animation 3 Part Animation of Ear Close Up.

9 Decibel Scale Decibels (db) Pressure (Atm) Example Threshold of hearing Whisper at 1 meter Study Hall Normal Conversation Busy Traffic Fire engine siren Rock concert Jet on carrier deck Prolonged exposure can cause moderate to permanent hearing loss.

10 Pitch is known as frequency. Human range of hearing: 20 Hz - 16,000 Hz Pitch Average person over 70 has lost the ability to hear frequencies above 8000 Hz. Which is why speech is hard to decipher for older people. Ultrasonic Frequencies above audible range Bats, ultrasound, dog whistles, cleaning Infrasonic Frequencies below audible range Earthquakes, elephants NOTE Freq (Hz) C C# D Eb E F F# G G# A Bb B C A = 440 Hz is used as the standard, and the interval between each note is 2 1/12 = C Blues: C Eb F G

11 How s Your Hearing Turn Your Speakers Up, and Click on the Speaker Icons below to find your Ringtone!! 8.0 KHz 16.7 KHz 10.0 KHz 17.7 KHz 12.0 KHz 18.8 KHz 14.1 KHz 19.9 KHz 14.9 KHz 21.1 KHz 15.8 KHz 22.4 KHz

12 Frequency (Hz) Frequency vs. Musical Note Value y = 0.623x x R 2 = C C# D Eb E F F# G G# A Bb B C

13 The Doppler Shift The Doppler Effect is experienced whenever there is relative motion between a source of waves and an observer. Occurs in all waves (mechanical and electromagnetic) Uses: Weather radar, police radar, ultrasounds, astronomy, NASCAR Toward Higher Frequency Away Lower Frequency Doppler Shift Animation Why Jets are never where they seem

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15 Breaking the Sound Barrier

16 Breaking the Sound Barrier

17 Breaking the Sound Barrier

18 Breaking the Sound Barrier

19 Sonic Boom A Sonic Boom is heard when something breaks the sound barrier. 343 m/s (767 mph) = Mach 1 Sonic Boom scientifically known as a Shockwave Bull whips and jets are other examples of supersonic speed; speed faster than sound. Ultimately, the farther a sniper can be from his target and still remain accurate the more effective he is and the less likely he is to be discovered. Using a 7.62mm round, snipers can shoot nearly silently as long as they're shooting from over 600 meters. A bullet leaves the rifle barrel faster than the speed of sound. The cracking sound a bullet makes is a tiny sonic boom. Even if a target doesn t hear the rifle shot, he will hear the bullet fly by. But the drag created by wind resistance on a 7.62mm round as it travels through the air slows the bullet down to subsonic speeds at around 600 meters. So at ranges over 600 meters, the bullet no longer makes that distinct cracking sound. Army Ranger Sniper tells us, "If you're shooting at a target 800 or 1,000 meters out, you could be shooting at that person all day long and they don't even know they are being shot at."

20 Speed Slang Mach 1: 1 x the speed of sound (343 m/s) Mach 2: 2 x the speed of sound (686 m/s) Subsonic: All speeds under Mach 1 Supersonic: All speeds over Mach 1 Hypersonic: All speeds over Mach 5 (3800 mph)

21 Sources of Sound Sound has to be produced by a vibrating object. Percussion: surface vibrates Brass instruments: lips vibrate Woodwind instruments: Reed vibrates Stringed instruments: Strings Vibrate Piped instruments: Column of air vibrates.

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23 Open Tube Resonator

24 Resonance in Air Columns Length of tube dictates pitch (frequency). Shorter = higher frequency 2 Types Open Pipe / Tube: Both ends open. Ex: Pan flute, Clarinet, Trumpet, Pipe organ Closed Pipe / Tube: One end closed. Ex: Soda bottle, flute

25 Open Tube Resonators If the end is open, the elements of the air have complete freedom of movement and an antinode exists Link to animation of Open Tube Resonance.

26 Open Tube Resonators In a pipe open at both ends, the natural frequency of vibration forms a series whose harmonics are equal to integral multiples of the fundamental frequency v ƒ n nƒ n 1, 2, 3, n 2L 1

27 Closed Tube Resonators If one end of the air column is closed, a node must exist at this end since the movement of the air is restricted Link to animation of Closed Tube Resonance.

28 Closed Tube Resonators The closed end must be a node The open end is an antinode v ƒ 1, 3, 5, f n n n n 4L 1 There are no even multiples of the fundamental harmonic

29 Example Problem When a tuning fork with a frequency of 392 Hz is used with a closed pipe resonator, the loudest sound is heard when the column is 21 cm and next at 65.3 cm. The air temp. is 27 deg Celcius. What is the speed of sound at this temperature?

30 Sound Quality All 3 waves have same amplitude, period and frequency, but they have a different shape. Shape is Timbre or tone color / tone quality Consonance: When 2 notes sound good C Major Chord: C E G For past 2500 years, accepted as Sweetest 3 note chord Dissonance: When 2 notes sound bad Octave: When 2 notes have a frequency of 1:2

31 Beats Beats are alternations in loudness, due to interference Waves have slightly different frequencies and the time between constructive and destructive interference alternates The beat frequency equals the difference in frequency between the two sources: ƒ ƒ ƒ b 2 1