Sound

Chapter 15.1

Properties of Sound• Sound waves – Longitudinal Waves–Caused by vibrations–Carry energy outward, which hit your ear

Speed of Sound• Speed is determined by the medium! • Sound waves mechanical rely on a

medium (particles) for transfer of energy • Speed of sound fastest in solids, then liquids,

then gas

Loudness• Loudness is determined by the intensity of sound

waves (rate at which waves transmit energy through an area)

• Intensity measured in decibels, dB • Quietest sound humans can hear 0 dB • Constant exposure to 120 dB and above can cause

permanent deafness

Pitch• Pitch measure of how high or low a sound is – Pitch is related to the frequency of sound waves– High pitch = high frequency (more # vibrations) – Low pitch = low frequency (low # vibrations)

Frequency Range• Humans hear sound waves in a limited

frequency range: 20 Hz to 20,000 Hz • Sound below 20 Hz is known as infrasound • Sound above 20 Hz is known as ultrasound

Hearing• The ear senses vibrations, amplifies (increases)

them, and transmits the signals to the brain • Three regions vibrations pass through: outer,

middle, and inner• Eardrum sends vibrations to inner ear to the

cochlea • Brain interprets vibrations from cochlea

Sonar• Sounds can be reflected and come bounce back to

you (ex: echoes!)• Sonar uses reflection for navigation • SONAR Sound Navigation and Ranging a

system that uses acoustic signals and echo returns to determine the location of objects or to communicate

Sonar• Sonar determines distances by measuring the

time it takes for sound waves to be reflected back from a surface

• Ultrasound waves (frequencies above 20,000 Hz) work well with bat sonar because of the fast traveling waves help bats to navigate and locate food!

Ultrasound imaging in medicine

• Ultrasound can be used to produce sonograms (pictures of a baby inside the body)

• Frequencies are sent in and reflected back to determine where the fetus is and the positioning

Sound Check!