Sound
•Vibrations that travel through the air or other media •When these vibrations reach the air near your ears you hear the sound. How Sound Travels •Sound waves carry energy through a medium (solid, liquid or gas) without the particles of the medium traveling along. •Sound travels as a longitudinal wave. How Sounds are Made •Longitudinal waves are generated when a source of energy forces the matter in a medium to vibrate. •This back-and-forth motion pushes air particles together, generating a compression, or moves the particles apart, generating a rarefaction. Medium •Sound waves must have a medium to travel through. •Gas – air is the most common •Liquid •Solid •In outer space there are no molecules to compress or rarefy, so sound does not travel through outer space. Speed of Sound •Depends on the physical properties of the medium it travels through. •Elasticity •Density •Temperature •At room temperature, sound travels through air at about 342m/s. Physical Properties of Media •Elasticity – the ability of a material to bounce back after being disturbed •Solid materials are usually more elastic than liquids or gases. •Particles of a solid do not move very far, so they bounce back and forth quickly as the vibration travels through the object, which allows waves to move faster. •Density – how much matter there is in a given amount of space •The speed of sound depends on how close together the particles of the substance are in the medium. •Temperature - degree or intensity of heat present in a substance or object •In a given media (solid, liquid, gas), sound travels more slowly at lower temperatures. Properties of Sound Waves •Intensity •Loudness •Frequency •Pitch •Intensity – the amount of energy the wave carries per second through a unit of area •Amplitude increases with increased energy •Measured in watts per square meter (W/m2) •Loudness – describes what you actually hear. •Though not the same as loudness, the greater the intensity of a sound wave, the louder it is. •Measured in decibels (dB) •Maximum safe level is 85 dB Frequency – the number of vibrations that occur per second Wavelength changes with frequency Measured in Hertz (Hz) 50Hz = 50 vibrations per second •Pitch – a description of how high or low the sound seems to a person •High frequency = high pitch •Low frequency = low pitch •Example: a young girl might have a squeaky (high pitched) voice, an older man might have a deep (low pitched) voice Doppler Effect •The apparent change in frequency as a wave source moves in relation to the listener •Sounds moving toward a person – Waves are at a higher frequency, so pitch appears to increase (high) •Sound moving away from a person – Waves are at a lower frequency, so pitch appears to decrease (low) Comments are closed.
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Erik E. Mason
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