# Sound

## Physical Science - Middle School

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How We Hear Compression Rarefaction Compression wavelength wavelength auditory nerve middle ear bones cochlea eardrum The farther sound travels, the less intense it becomes. At a distance of 2 m, sound is heard at 1/4 the intensity heard at 1m. Speed of Sound Medium Speed (m/s) air (0ºC) 331 air (20ºC) 343 air (100ºC) 366 water (20ºC) 1,482 steel (20ºC) 5,200 Sound is created by the vibrations of an object. A vibration is a complete back-and-forth motion by an object. The object could be a guitar string, a drum, the diaphragm of a loudspeaker, or even your vocal cords. Sound travels through a medium as longitudinal waves. Longitudinal waves are made of compressions and rarefactions. The media that sound travels through include air, water, glass and metal, among others. As the drum skin vibrates, it moves forward and pushes the air particles in front of it closer together, creating an area of higher density and pressure called a compression. As the drum skin retracts, air particles close to the drum skin become less concentrated, creating an area of lower density and pressure called rarefaction. With each vibration, a compression and rarefaction are formed. As they travel away from the drum, sound is transmitted through the air. Properties of Sound The Speed of Sound Sound travels at different speeds through different matter. In general, the denser the matter, the faster sound travels through it. Pitch and Frequency The pitch of the sound determines how low or high a sound seems to be. The pitch of a sound depends upon the frequency of the vibrations that cause it. The frequency of a sound is the number of vibrations per second. The frequency of sound is measured in units called hertz (Hz). Loudness and Amplitude The loudness of a sound depends upon the amplitude (height of a sound wave) of the vibrations that cause it. Sound travels as sound waves. The bigger the vibration, the greater the amplitude of the waves, and thus the louder the sound will be. The loudness of sound is measured in units called decibels (dB). Sound waves enter the ear and cause the eardrum to vibrate. Three small bones in the middle ear carry these vibrations to the cochlea (pronounced "kok-lee-a"). The cochlea contains tiny hairs, which send messages to the brain that are interpreted as sound. Humans normally are able to hear frequencies between 20 and 20,000 Hz. Sounds above this frequency are referred to as ultrasound. frequency wavelength amplitude crest trough time 1 m 2 m Sound © Copyright NewPath Learning. All Rights Reserved. 94-4809 www.newpathlearning.com Decibels of Sound 25 dB 60 dB 100 dB 115 dB 140 dB cat purring normal conversation train horn rock concert jet plane 2,000 to 110,000 bat 45 to 64,000 cat 16 to 12,000 elephant 20 to 20,000 human 67 to 45,000 dog Frequencies Heard by Animals Animal Frequency range (Hz)
\|xiBAHBDy01807qzZ How We Hear wavelength auditory nerve middle ear bones eardrum Speed of Sound Medium Speed (m/s) air (0ºC) 331 air (20ºC) 343 air (100ºC) 366 water (20ºC) 1,482 steel (20ºC) 5,200 Sound is created by the ________________ of an object. A ________________ is a complete back-and-forth motion by an object. The object could be a guitar string, a drum, the diaphragm of a loudspeaker, or even your vocal cords. Sound travels through a media as ________________ ____________ . Longitudinal waves are made of ________________ and ________________ . The media that sound travels through include __________ , __________ , __________ and __________ , among others. As the drum skin vibrates, it moves forward and pushes the air particles in front of it closer together, creating an area of higher density and pressure called a _____________________ . As the drum skin retracts, air particles close to the skin become less concentrated, creating an area of lower density and pressure called _____________________ . With each _____________________ , a compression and rarefaction are formed. As they travel away from the drum, sound is transmitted through the _____________________ . Properties of Sound The Speed of Sound Sound travels at different _______________ through different matter. In general, the ______________ the matter, the ______________ sound travels thro ugh it. Pitch and Frequency The ______________ of the sound determines how low or high a sound seems to be. The pitch of a sound depends upon the _________________________________ that cause it. The frequency of a sound is the number of vibrations per second. The ______________ of sound is measured in units called ______________ . Loudness and Amplitude The loudness of a sound depends upon the _________________ of the vibrations that cause it. Sound travels as ____________ ____________ . The bigger the vibration, the greater the _________________ of the waves, and thus the louder the sound will be. The loudness of sound is measured in units called _________________ . 1 m 2 m Describe how we hear: ____________________________________________________________________ ____________________________________________________________________ ______________________ ______________________ ______________________ ______________________ ______________________ ______________________ ______________________ ______________________ Key Vocabulary Terms amplitude cochlea compression crest decibel eardrum frequency hertz longitudinal wave loudness middle ear bones pitch rarefaction sound trough ultrasound vibration wave wavelength time Sound © Copyright NewPath Learning. All Rights Reserved. 94-4809 www.newpathlearning.com Decibels of Sound 25 dB 60 dB 100 dB 115 dB 140 dB cat purring normal conversation train horn rock concert jet plane