Sound

• Sound is a mechanical wave.
• Sound waves come from a vibrating source e.g. loudspeaker
• A loudspeaker makes noise by the cone vibrating. It moves forwards and backwards, which squashes & stretches the air in front. As a result, a series of compressions (squashes) and rarefactions (stretches) travel out through the air, these are sound waves
• Humans can hear frequencies between 20 and 20000 Hz.
• Ultrasound Waves: high frequency sound waves, medically used to look at structures and organs inside the human body, i.e. to form an image of a fetus in a pregnancy
• • Compression: High pressure section of a longitudinal wave
  • Rarefaction: Low pressure section of a longitudinal wave

  
• The higher the frequency, the higher the pitch

  
• The higher the amplitude, the louder they sound

  
• If a sound is repeated 0.1 seconds or more after it is heard, the brain senses it again

  
• If a sound reflects off a surface a long way away, an echo can be heard (after 0.1 seconds)
• Sound varies speed in different media. For example:

  1. Solid: 5000 m/s in concrete
  2. Liquid: 1400 m/s in water
  3. Gas: 330 m/s in air