Sound

Sound Travels as a longitudinal wave Series of compressions and rarefactions Anything that vibrates produces a sound

Speed of Sound Depends on properties of the medium Elasticity, temperature, and density Lower temperatures = slower waves Some sounds are lower at some temperatures Average speed is 343 m/s Chuck Yeager flew at 293 m/s and is said to have flown faster than the speed of sound…how is this true??

He was at an altitude of 12,000 meters Speed of sound at that height (lower temperature) is 290 m/s http://www.chuckyeager.com/

Speed of Sound The speed of sound in air changes with temperature. The speed at 0oC is 331m/s for dry air It increases by 0.6 m/s for each degree Celsius above zero.

The speed of sound also depends upon the medium. Sound needs a medium through which to travel. Sound cannot travel through the vacuum of space. Space is silent (no matter what you hear in the movies). Sound travels faster through a solid and liquids than through air. WHY? Proximity of particles and their movement

Elasticity and Density Fastest through solids and slowest through gases Solids are more elastic than liquids and gases In 2 materials that are in the same state, sound travels fastest through the less dense subject.

Frequency and Pitch Pitch Depends on the frequency of the wave How high or low a sound is Depends on the frequency of the wave High pitch = high frequency Treble, a high soprano may have a frequency of 1000 Hz Low pitch = low frequency Bass, thunder has a frequency of 50 Hz

What can we hear???? Human ears can hear 20 TO 20,000 Hz Hearing Test

Hearing and the Ear Vibrations are amplified by the 3-bones in the middle ear ( that form a lever system ) to push waves into the inner ear (hammer/anvil/stirrup) The inner ear ( basilar membrane vibrates  hair fibers stimulate nerve fibers that send impulses to the brain. The brain interprets the impulse as sound.

ULTRASONIC Frequencies above 20,000Hz Many animals can hear frequencies above this Dogs = 35,000Hz Cats = 65,000 Hz Porpoises = 150,000Hz Bats make ultrasonic sounds that echoes off of caves, etc.

Infrasonic Frequencies below 20 Hz Elephants communicate this way Earthquakes, volcanoes, and some machinery gives off infrasonic sounds

The Doppler Effect The change in wave frequency due to a moving wave source is called the Doppler Effect. The Doppler Effect is observed when the source of sound is moving relative to the observer.

The Doppler Effect

Loudness & Intensity Loudness is the human perception of sound intensity. Intensity is the amount of energy in each wave. Greater Energy = Greater Amplitude Therefore, Intensity is determined by amplitude. Big wave = Loud Small wave = Soft

Amplitude is related to Intensity Characteristics Loudness is related to Amplitude Amplitude is related to Intensity

Intensity Measured in dB 0 dB can barely be heard Human ear has a pain threshold of 120 dB Music above 85 dB can damage ears

The Decibel Scale

Acoustics Acoustics is the study of sound. The effect produced by many reflections is called reverberation. Soft porous materials and certain room shapes can reduce excess reverberation. Acoustic scientists work on understanding human hearing and speaking.

COMBINING SOUNDS CONSTRUCTIVE INTERFERENCE – SOUND WAVES COMBINE SO THAT RESULTING DISTURBANCE IS GREATER THAN EITHER SOUND WAVE WAS BEFORE THIS IS WHY SOUNDS ARE LOUDER IN AMPIHTHEATERS – THE WAVES BOUNCE OFF THE WALLS AND COMBINE DESTRUCTIVE INTERFERENCE – SOUND WAVES COMBINE SO THAT THE RESULTING DESTRUCTION IS SMALLER THAN EITHER WAVE WAS BEFORE THE SOUND IS SOFTER DEAD SPOTS ARE AREAS IN LARGE HALLS WHERE LITTLE SOUND CAN BE HEARD BECAUSE OF DESTRUCTIVE INTERFERENCE

Beats A “BEAT” OCCURS WHEN 2 WAVES OF SLIGHTLY DIFFERENT FREQUENCY ADD TOGETHER - EVERY FEW CRESTS OR TROUGHS LINE UP 24-4 QUALITY AND SOUND

Sonar SONAR IS HIGH-FREQUENCY ULTRASONIC WAVES THAT ARE USED IN A SYSTEM CALLED Sound Navigation And Ranging RESEARCH SHIPS SEND SOUND WAVE INTO WATER THAT TRAVELS IN A STRAIGHT LINE UNTIL IT HITS AN OBJECT THE WAVE IS THEN REFLECTED BACK TO THE SHIP THE TIME IT TAKES TO TRAVEL BACK AND FORTH IS MEASURED AND USED TO CALCULATE THE DISTANCE TRAVELED USED IN COMMERCIAL FISHING TO LOCATE FISH USED TO FOCUS AUTO-FOCUS CAMERAS USED TO FIND OIL MINERALS INSIDE THE EARTH

ULTRASONIC CLEANING ULTRASONIC WAVES ARE USED TO CLEAN DELICATE ITEMS LIKE JEWELRY, ELECTRONICS, AND SURGICAL INSTRUMENTS. THE VIBRATIONS KNOCK OFF DEBRIS WITHOUT DAMAGING THE ITEM

Sound and Medicine ULTRASOUND IMAGING – ULTRASONIC WAVE IS SENT THROUGH THE BODY AND REFLECTS OFF BONES AND ORGANS THESE ARE SAFER THAN X-RAYS, WHICH CAN ALTER CELLS ULTRASONIC WAVES ARE ALSO USED TO TREAT PROBLEMS USED TO BREAK UP KIDNEY STONES SO THAT THEY ARE EASIER TO PASS USED TO TREAT INJURED MUSCLES

An echo is a reflected sound wave Echoes An echo is a reflected sound wave An echo travels to a barrier and then reflects back What materials are used to reduce echoes in buildings? Acoustical tiles

Resonance - Demo Resonance – when the frequency of the stimulus (wave) is the same as the object - ( material it is made of ) View: Tacoma Narrows Bridge Collapse Fundamental Frequency – lowest frequency possible of a harmonic series Harmonics – ( also called Overtones) vibrations that are multiples of the fundamental frequency.

Harmonics and Overtones 1st harmonic = fundamental frequency 2nd harmonic = 1st overtone 3rd harmonic = 2nd overtone 4th harmonic = 3rd overtone and so on...

Sound Interference – Interference of sound waves produce BEATS

Music vs. Noise You hear alternating loud and soft sounds. Sound quality or timbre is the blending of pitches to produces sound Music Instrumental and vocal tones – sound waves in a structured or regular pattern Noise Sound waves with irregular vibration and no definite pattern

Standing Waves Caused by the interference of two identical waves (or a wave and its reflected wave) travelling in opposite directions in a medium. Wave pattern of alternating nodes and antinodes. Nodes - areas of no displacement of the medium caused by destructive interference Antinodes - areas of maximum displacement of the medium caused by constructive interference. Note: One wavelength (shown in the diagram) is equal to twice the distance between nodes. node Antinode

Music Pleasing quality, definite identifiable pitch, repeated time (rhythm) All instruments create a vibration String instruments – tighter string - higher pitch Woodwind/brass instruments - column of air vibrates Percussion – vibrates by being struck