P1.5.3 Sound

P1.5.3 Sound

1. Sound waves are longitudinal waves and cause vibrations in a medium

   • which are detected as sound
   • they cannot travel through a vacuum (e.g is space)
   • the frequency of the normal human ear is from about 20Hz to about 20000 Hz
     • Ultrasonic waves are those with a frequency greater than 20000Hz, the upper frequency limit of the human ear

2. 1) Vocal cords vibrate and produce sound every time you speak

   • 2) Any object vibrating air makes the layers of air near the object vibrate
     • 3) These layers in turn make the layers of air further away vibrate
       • 4) the vibrating object pushes and pulls repeatedly on the air
         • 5) this sends out vibrations of the air in waves of compressions and rarefractions
           • 6) When the waves reach your ears, they make your eardrums vibrate in and out so you hear sound as a result

3. The pitch of a sound is determined by its frequency

   • The loudness by amplitude

4. Echoes are reflections of sounds

   • no echoes when
     • soft fabric -absorbed
     • uneven surface- reflected sound is broken up and scattered

5. Refraction of sound

   • The warmer the air is, the greater the speed of sound
     • Refraction takes place at the boundaries between layers of air at different temperatures
       • At night: you can hear a sound a long way from its source as sound waves refract back to the ground instead of travelling away from the ground
         • In the daytime: sound refracts upwards, not downwards, as the air near the ground is warmer than air higher up