 Sound waves are longitudinal waves.
 Sound requires medium tor travel.
 Sound cannot travel through vacuum.
 Study of sound is known as acoustics.
 Echo and reverberation are due to the reflection of sound. For the
production of echo there should be a minimum distance of 17m between
us and the reflecting surface.
 Bats can fly in the dark because they can generate ultrasonic sound and if
there is any hindrance in their way the sound wave get reflected and they
can change their direction.
 The audible frequency of human ear is between 20 hertz and 20000 hertz.
 Velocity of sound in the air is 340 m/s.
 Sounds are distinguished from each other by pitch (frequency), loudness
(intensity) and quality.
 Phonogram is a machine to reproduce sound.
 The speed of sound depends on the medium the waves pass through.
 SONAR stands for sound Navigation and ranging. It uses ultrasonic waves.
 Velocity of sound in moist air is greater than in dry air.
 Sound travels faster in steel.
 The intensity of sound is measure in decibel.
 During night the allowed intensity of sound in hospital area is 40db.
 Ultrasonic sounds can be received and emitted by bats. While infrasonic
sound can be received by snakes.