Chapter 2: Sound Section 2: Properties of Sound Do Now: 1.Copy homework 2.Cornell Notes FQs: Why are sounds loud or soft? Why are sounds high or low?

Two Main Properties of Sound  Loudness: Your perception of the energy of a sound Your perception of the energy of a sound  Pitch: The description of how high or low a sound seems to a person The description of how high or low a sound seems to a person

Loudness  Your perception of the energy of a sound  Depends on two factors: Energy used to make the sound Energy used to make the sound Distance from the source of the sound Distance from the source of the sound  Energy Pull back on a rubber band Pull back on a rubber band Pull back even farther - louder Pull back even farther - louder

Loudness  Distance Talk to person next to you Talk to person next to you Lean in closer – louder Lean in closer – louder Close to source, wave covers small area Close to source, wave covers small area Wave travels away and covers larger area Wave travels away and covers larger area Intensity: the amount of energy a sound wave carries per second through a unit area

Loudness  Measuring loudness Unit: decibel (dB) Unit: decibel (dB)  Each 10dB increase represents a tenfold increase in intensity  30dB is ten TIMES louder than 20dB  30dB is 100 TIMES louder than 10 dB  Sounds louder than 100dB can damage your hearing Sound Loudness (dB) Rustling leaves 10 Whisper15-20 Very soft music Normal conversation Heavy street traffic Loud music Rock concert Jackhammer120 Jet plane takeoff

Pitch  The description of how high or low a sound seems to a person  Depends on the frequency of the wave

Pitch  Frequencies: Bass singer: lower than 80 Hz Bass singer: lower than 80 Hz Soprano singer: higher than 1,000 Hz Soprano singer: higher than 1,000 Hz Most people can hear between 20 and 20,000 Hz Most people can hear between 20 and 20,000 Hz Above 20,000 = ultrasound Above 20,000 = ultrasound Below 20 = infrasound Below 20 = infrasound How’s your hearing? How’s your hearing? this-hearing-test/ this-hearing-test/ this-hearing-test/ this-hearing-test/

Pitch  Music uses specific pitches called notes  Change pitch using vocal cords, located in larynx (voice box)  Vocal cords can vibrate more than 1,000 times per second  Stretch and relax cords for different notes  Stretch – vibrate more quickly (higher frequency, higher pitch)  Relax – vibrate more slowly (lower frequency, lower pitch)  Same as guitar string

The Doppler Effect  The change in frequency of a wave as its source moves in relation to an observer Austrian scientist Christian Doppler ( ) Austrian scientist Christian Doppler ( )  If sound waves, heard as a change in pitch  If light waves, seen as “red shift”  Motion of source adds to motion of waves

Shock Waves  Shock waves are caused by the Doppler effect  The science behind shock waves is pretty advanced and difficult to understand. Maybe you could make it a journal question….