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Sound Waves Chapter 11 Section 1 Sound Waves • Sound waves are compressional waves • Sound waves require a medium • The medium can be a solid, liquid, gas, or another combination of the three • In general, sound waves travel slowest in gases and fastest in solids • Sound waves also travel faster at higher temperatures – Why? • Because the molecules and atoms are already colliding more frequently The Speed of Sound • When a tuning form makes sounds waves – The wave forms a compression when the tuning fork tine moves inward (c) – The wave forms a rarefaction when the tuning fork tine moves outward (b) Amplitude and Energy • The amount of energy carried by a wave is directly related to the amplitude of the wave. • As amplitude increase, energy increases • In a compression wave, denser compressions and more disperse rarefactions are associated with high amplitude Amplitude and Energy • The amount of energy transferred by a sound wave through a medium each second is the intensity. • High amplitude = high intensity = high energy • Intensity decreases as the waves travel away from the source – Intensity decreases as sound waves spreads out Amplitude and Loudness • Your ears and brains can detect changes in intensity • Loudness is the human perception of sound intensity • As intensity increases, loudness increases A Scale For Sound Intensity • There is a scale for sound intensity • Each unit on the scale is a decibel (dB) – 0 dB is the faintest sound that most people can hear – Sounds above 120 dB may cause pain and permanent hearing loss A Scale for Sound Intensity • There is no cure for noise induced hearing loss; therefore, prevention is important Pitch and Frequency • Pitch is the human perception of the frequency of sound waves • Pitch increase as frequency increases – Frequency is the measure of how many compressions pass a fixed point in one second • The human ear can usually hear frequencies between 20 Hz and 20,000 Hz – The ear is most sensitive to sounds between 440 Hz and 7000 Hz Pitch and Frequency Ultrasonic Waves • Waves about 20,000 Hz are called ultrasonic waves – Can’t typically be heard by the human ear – Dogs can usually hear up to 35,000 Hz – Bats can hear more than 10,000 Hz – Used in medicine for diagnostics and treatment – Also used in depth detectors Infrasonic Waves • Waves with frequency below 20 Hz • The frequency of these waves vibrate very slowly – Earthquakes, wind, heavy machinery • Even when they can’t be heard, you can often feel them Doppler Effect • When an object making sound is at rest, sound waves radiate out from the object with equal wavelength in all directions. • A person in front of the object will “see” the same wavelength as a person behind the object Doppler Effect • Now lets consider a object in motion • The moving object begins to catch up to the waves in front of it causing them to bunch up. • The observer in front will experience the bunched up waves (high frequency) • The observer behind the object will experience less dense waves (lower frequency Supersonic • When the object is moving faster than the speed of sound, the observer will hear the sound after the object has passed • The sound that results is a sonic boom • Supersonic Flight Using Sound • Curing Cancer • Boiling Water • Healing Wounds • Growing Food • Revealing Natural Geometry • Stabilizing Braining Waves • Cancelling Sound • Levitation • Echolocation • Ultrasound 10 Amazing Uses of Sound