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

Intensity and Loudness Intensity: the amount of energy that flows through a certain area in a specific amount of time Loudness: human perception of sound intensity (measured on a loudness scale in decibels (dB) human hearing can be damaged by sounds over 120dB. Increased intensity = increased loudness

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

Uses of Sound Sounds provide many everyday uses such as… music, entertainment, sirens, fire alarms, warning signals, bells for timers etc.

Acoustics Acoustics- the study of sound, sometimes there is an echoing effect produced by many reflections of sound. This is called reverberation. Walls of auditoriums, concert halls, etc. should be lined with material that reduce reflection-like carpets and draperies.

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