Sound waves

• Sound is caused by vibrations. Vibrating particles pass on energy to particles next to them. Sound is a longitudinal wave.
• The larger the amplitude the louder the sound.
• The higher the frequency, or shorter wavelength, the higher the pitch of the sound.
• How does sound travel?

  1. An objects makes a sound by vibrating
  2. The vibrations pass through by making air molecules vibrate
  3. These vibrations are picked up by the ear
• Humans can hear from 20-20,000Hz. Anything above is called an Ultrasound, anything below is called an infrasound.
• Distance= speed x time.
• Speed of sound in water is 1500m/s
• The time in distance= speed x time is the time for the reflected wave to come back.
• How does a transducer work?

  • It emits a pulse of ultrasound
  • The sound wave passes through the medium. Some waves are reflected at the boundary between two media
  • The time for the reflected waves to return is measured
  • The depth of the boundary is calculated using time and speed of sound in the medium
• An ultrasound is safer than an x-ray because it is not ionizing. It also has a real-time image.
• Seismic waves are the waves that travel through the earth and are caused by earthquakes.
• Primary seismic waves are longitudinal waves that refract at the boundary between the mantle and outer core. This is because their speed changed abruptly at the boundary.
• Secondary seismic waves are transverse waves and so they can't travel though the liquid outercore.
• Primary waves: pass through a solid and a liquid

  Secondary waves only pass through solid. Blocked by liquid outer core.
• Why do seismic waves curve?

  Because of the refraction caused by the changes in density.