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