Sound

• Compression is a region where the air particles are closer together, resulting in air pressure higher than normal atmospheric pressure.
• Rarefaction is a region where the air particles are further apart, resulting in air pressure lower than normal atmospheric pressure.
• Loudness relates to amplitude.
• Pitch relates to frequency.
• audible and inaudible sound:

  infrasound: 0-20Hz

  human: 20-20000Hz

  dogs: 20-100000Hz

  ultrasound: 20000-1000000+Hz
• Reflection of sound is called an echo.
• Sonar (sound, navigation and ranging) technology, imaging internal organs and breaking up kidney stones and cancer treatment are all under ultrasound.
• Sound waves are a longitudinal wave which needs a medium to propagate
• Sound waves can measure the depth of sea floor, find fishes, medical imagine and breaking up kidney stones