Sound and Related Topics Let’s Hear More About It

Sound “ideas” b compression -- molecules are squished together creating areas of high pressure. b rarefaction -- molecules are spread apart creating areas of low pressure. b Compressional wave with air as the medium

Example:

Sound waves need three things: b A source ; something vibrating. b A medium; something for the wave to travel in. b A receiver; something to detect the vibration.

If the vibration is: b Regular and pleasing, we call it music b Irregular and annoying, we call it noise.

The medium dictates the velocity: b Fastest in more dense mediums, and more elastic mediums. b Fastest in more dense mediums, and more elastic mediums. [bucket] b ~ miles/hour b In air sound travels at ~331.5m/s at 0 o C, and increases with Temperature. b In some solids, it can travel at ~5000 m/s. b TOOLBOX: Speed of Sound 340 m/s b In water it travels at ~ 1500m/s, while b MACH 1

Speed of Sound in Various Materials Gases Material v (m/s) Hydrogen (0°C)1286 Helium (0°C)972 Air (20°C)343 Air (0°C)331

Liquids Liquids at 25°C Material v (m/s) Glycerol1904 Sea water1533 Water1493 Mercury1450 Kerosene1324 Methyl alcohol1143 Carbon tetrachloride926

Solids Solids Material v (m/s) Diamond12000 Pyrex glass5640 Iron5130 Aluminum5100 Brass4700 Copper3560 Gold3240 Lucite2680 Lead1322 Rubber1600

Sonic BOOM b A Sonic boom is a noise similar to thunder. It is caused by an object moving faster than sound. b An aircraft traveling through the atmosphere continuously produces waves similar to the water waves boat. When the aircraft exceeds the speed of sound, these pressure waves combine and form shock waves. As an aircraft flies at supersonic speeds it is continually generating shock waves, dropping sonic boom along its flight path, similar to someone dropping objects from a moving vehicle. If the plane makes a sharp turn or pulls up, the boom will hit the ground in front of the aircraft.

Sonic BOOM

Sound Wave Characteristics:

Wavelength: b The distance between 2 successive compressions (or 2 successive rarefactions).

Amplitude: b Relates to the intensity or loudness of the sound. b An indication of the energy of the wave.

Amplitude: b Measured in units called decibels (dB’s). 120 dB’s is the human ear’s pain threshold

Frequency: b Relates to the pitch (or tone). b The higher the frequency, the higher the pitch.

The human ear. b Very detailed construction. b Range is from 20 hertz to 20,000 hertz.. b Below 20 Hz -- infrasonic sounds. b Above 20,000 Hz -- ultrasonic,

Uses of Sound

Infrasonic (Subsonic) b sound frequencies below 20 Hz b Earthquakes produce infrasonic sound b Elephants communicate through infrasonic b VERY LOW SOUNDS

Ultrasonic b sound frequencies above 20,000 Hz b Examples: SONAR b Examples: Echolocation – Bats, Whales b Medical Uses

SONAR b (So)und (Na)vigation and (R)anging b Can be used over long distances b 4 sites cover 80% of the ocean b Sound sent underwater, bounces back

RADAR b (Ra)dio (D)etecting (a)nd (R)anging b Radio waves – Not Sound Waves b We’ll come back to this topic during EM waves

Sound Wave Phenomena

Doppler Effect b A Change in pitch or frequency due to a moving wave source. b In front of object: High frequency, high pitch, short wavelength b Behind object: Low frequency, low pitch, long wavelength. b Sound waves get pushed together, or spread out, changing pitch

Doppler Effect b Doppler Effect Applet Doppler Effect Applet Doppler Effect Applet

Resonance: b When the vibration of the source matches the natural frequency of the object, causing it to start resonating (vibrating). b Resonance is Vital to the proper functioning of most musical instruments. b All objects have a natural frequency

Resonance: b Objects vibrate more and more as they absorb more natural frequency vibrations (constructive interference). If they absorb enough energy, they will break.

How You HEAR!! b The outer Ear: Where sound waves are gathered -Visible part (pinna) -Visible part (pinna) -Ear Canal -Ear Drum Channel sound waves to eardrum which vibrates

How You HEAR!! b Vibrating ear drum causes 3 tiny bones to vibrate, which amplify the sound. -Hammer-Anvil-Stirrup b The Middle Ear : Sound is amplified

How You HEAR!! b The Inner Ear: Converts vibrations to nerve impulses - Cochlea Auditory Nerve Semi Circular Canals Eustachian Tube b Vibrations from middle ear vibrate the cochlea, which converts vibrations to nerve impulses

How You HEAR!!

Hearing Problems b Hearing Loss: tiny hairs (cilla) in cochlea are destroyed or damaged, often by loud sounds. b Deafness: Caused by failure of eardrum or tiny bones to vibrate. Problems with cochlea. b b Dizziness: Caused by problems with semi circular canals - Vertigo b Ear Infection – Eustachian tube is close to nasal cavity b Ear Infection – Eustachian tube is close to nasal cavity

MUSIC b Noise – random waves frequencies, and pitches b Music – sound in a regular pattern

Music b Every Musical note has a certain frequency, which gives it a distinct pitch. b Arrange the notes in a familiar or pleasing pattern and……

Music b Musical instruments contain strings, membranes, columns of air – something that vibrates at a natural frequency to create pitch. b Remember Resonance - Musical instruments contain a resonator which amplifies the sound.

Fundamentals and Overtones: b Fundamental Frequency : The lowest frequency. b Visit the Sound Lab Visit the Sound Lab b Overtones: Also called harmonics, these frequencies are whole number ratios of the fundamental

Sound Quality: b Quality: differences among sounds of the same pitch b Middle C for a Flute versus a Piano

Sound Quality b The overall sound “envelop” (the combination of the fundamental and overtones) makes the sounds distinguishable

Interference; b When two sound waves meet at the same time and spot. b The effect is called Beats: A rhythmic variation in amplitude. b Visit the Sound Lab Visit the Sound Lab Visit the Sound Lab b Beat Frequency = Difference in the two frequencies.

The end of the the story.