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Sound
The Nature of Sound
• Things vibrate (move back and forth) when they make sound.
• Sound travels as a longitudinal wave (series of compressions and rarefactions)
• Sound MUST have a medium to vibrate; without a medium there can be no sound (because nothing is vibrating)
Speed of Sound
• Speed of sound depends on 3 factors:– Temperature (kinetic energy of molecules)
• Lower temp –slower sound• Higher temp –faster sound
Speed of sound
• Elasticity (ability to move out of position and then go back)– Lower elasticity-slower sound– Higher elasticity- faster sound
• Solids are more elastic-so sound moves faster• Gases are less elastic-so sound moves slower
Speed of Sound
• Density- (compactness)- for materials is the same state– Lower density- faster sound– Higher density- slower sound
Frequency and Pitch• Frequency: number of wavelength that
pass a point per second (measured in hertz-Hz)
• Pitch: how high or low a sound seems to be– Increased frequency = higher pitch– Humans can hear sounds between 20 -
20,000Hz (subwoofer – 20 to 300 Hz)– Dogs can hear up to 40,000Hz– Bats can hear up to 100,000Hz
Ultrasonic Waves
• Ultrasonic Waves: sounds above 20,000 Hz– Used in medical diagnoses and treatment– Estimate size, shape and depth of underwater
objects
Infrasonic Waves
• Infrasonic Waves- sounds below 20 Hz– Even though you can’t “hear” these sounds
you may “feel” them as a rumble inside your body
Echolocation
• Echolocation- process of locating objects by emitting sounds and interpreting the sound waves that are reflected back.
Sonar
• Sonar- a system that uses sound waves to detect objects. (sound waves are sent underwater and the reflected wave is picked up by a microphone)
Ultrasound
• Ultrasound-used for cleaning and in medicine. Ultrasonic waves can be sent into a person’s body. Reflected ultrasonic waves are used to detect and monitor conditions such as pregnancy, certain types of heart disease, and cancer
Doppler Effect
• Doppler Effect- the change in pitch or wave frequency when a sound and its receiver move relative to one another– Move closer together- higher frequency and
pitch– Move further apart –lower frequency and pitch
• Rader guns- use Doppler to measure speed• Weather Doppler- shows movement of winds in
storms