Sound Origin of Sound Nature of Sound in Air Media that Transmit Sound Speed of Sound in Air Refraction Energy in Sound Waves Forced Vibrations Natural Frequency Resonance Interference Beats

Sound... ...a longitudinal wave in air caused by a vibrating object. Sound requires a medium. solid, liquid or gas Will a bell ring in a evacuated Bell Jar?

Nature of Sound in Air Sound waves have compression and rarefaction regions.

Origin of Sound infrasonic ultrasonic human hearing range frequencies < 20 Hz ultrasonic frequencies > 20,000 Hz human hearing range frequencies between 20 Hz and 20,000 Hz

Speed of Sound in Air 340 meters/second 760 miles/hour Mach 1

SPEED OF SOUND increases with humidity How it varies: increases with temperature increases with density How it varies:

Lightning and Thunder What is the approximate distance of a thunderstorm when you note a 3 second delay between the flash of the lightning and the sound of the thunder?

What is the approximate distance of a thunderstorm when you note a 3 second delay between the flash of the lightning and the sound of the thunder? Answer: 3 seconds  340 meters/second = 1020 meters

Acoustics... ...the study of sound properties. When a sound wave strikes a surface it can be.… (a) reflected. (b) transmitted. (c) absorbed. (d) all of these.

 Acoustics... ...the study of sound properties. When a sound wave strikes a surface it can be.… (a) reflected. (b) transmitted. (c) absorbed. (d) all of these. 

Reflection of Sound e.g. an echo Reverberation - re-echoed sound, multiple reflections of sound waves from walls Compare reflections from a hard wall with that from a carpet wall.

Refraction of Sound Refraction - the bending of a wave Sound travels faster in warm air than in cool air. Sound waves bend toward cooler air.

Speed of Sound Subsonic - slower than the speed of sound Supersonic – faster than the speed of sound speed of object Mach Number = speed of sound

Forced Vibrations/Resonance …the setting up of vibrations in an object by a vibrating force. Examples of Forced Vibration: A tuning fork touching a wood surface Sounding boards for stringed instruments Matching tuning fork boxes

During forced vibration sound is intensified because a larger surface area is available to vibrate air molecules.

Resonances

Sound Interference Overlapping compressions of a sound wave will result in… …constructive interference. …and a louder sound. Overlapping a compression and a rarefaction results in... …destructive interference. …and a softer sound.

Destructive Interference Constructive Interference

Noise reduction headphones Echo cancellation Sound Interference Noise reduction headphones Echo cancellation

Beats Beats - the periodic variation in loudness of two sounds played together The beat frequency is equal to the difference in the frequency of the two sounds.

For the same temperature for air, does sound travel faster in humid Galveston or in dry El Paso? (a) Galveston (b) El Paso (c) same speed in either city

For the same temperature for air, does sound travel faster in humid Galveston or in dry El Paso?  (a) Galveston (b) El Paso (c) same speed in either city

The bending of sound through air of uneven temperature is called (a) reflection (b) refraction (c) interference (d) reverberation (e) resonance

The bending of sound through air of uneven temperature is called (a) reflection (b) refraction (c) interference (d) reverberation (e) resonance 

Lightning is seen, then ten seconds later thunder is heard Lightning is seen, then ten seconds later thunder is heard. Approximately, how far away in meters is the thunder cloud? (a) 10,500 m (b) 5280 m (c) 1050 m (d) 3400 m (e) 680 m

Lightning is seen, then ten seconds later thunder is heard Lightning is seen, then ten seconds later thunder is heard. Approximately, how far away in meters is the thunder cloud? (a) 10,500 m (b) 5280 m (c) 1050 m (d) 3400 m (e) 680 m 

A 250 Hz tuning fork and a 260 Hz tuning fork are vibrating near each other. How many beats per second are heard? (a) 255 (b) 510 (c) 10 (d) 250 (e) 260

A 250 Hz tuning fork and a 260 Hz tuning fork are vibrating near each other. How many beats per second are heard? (a) 255 (b) 510 (c) 10 (d) 250 (e) 260 

Musical Sounds

Noise Versus Music What is the difference between noise and music? Answer: The appearance of the waveform. Mac Mic

NOISE VERSUS MUSIC

Same Note - Different Instrument

Fundamental Frequency Harmonic a partial tone that is an integer multiple of the fundamental frequency Fundamental Frequency the lowest frequency of vibration a.k.a. the first harmonic

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Sound Intensity and Loudness Intensity of Sound refers to the amplitude of the pressure variations in the sound wave

Loudness the physiological sensation directly related to the sound intensity measured in bels 1bels = 10 decibels

Loudness A sound of 10 decibels is or 101 or 10 times as intense as 0 decibels. 20 decibels is 102 or 100 times the intensity 0 decibels. How much more intense is sound at 100 dB than sound at 50 dB? Answer: 100000 times

Source of Sound Loudness (db) Threshold of Hearing 0 Conversation 60 Ear Damage Begins 85 Amplified Music 110 Jet Airplane at 30 meters 140

Common Sound Intensities