Waves, hearing, exploration and detection

• Sound waves make solids vibrate
• sound waves are longitudinal waves
• Sounds waves cause compression and refraction because they are longitudinal waves.
• When a sound wave hits an object, its particles vibrate in the direction of wave travel
• Sound wave vibrations travel fastest through solids
• sound waves cannot travel through vacuum's because there are no particles to vibrate.
• Humans can hear sounds with frequencies between 20 Hz and 20 kHz
• This is because sound waves in solids can only be converted into vibrations over a limited frequency range.
• Sound waves can also be reflected and refracted.
• These properties make sound waves useful for detecting and observingthings we cannot see.
• Echo sounding uses high frequency sound waves to measure distances underwater
• Echoes are reflected sound waves
• Ultrasound waves can be used to form images
• Some ultrasound waves are reflected when they hit a boundary between two different materials.
• A detector can be used to measure how long it takes for the waves to be reflected
• Ultrasound waves are useful for medical imaging, for example scanning a foetus in the uterus and it is also useful for industrial imaging, for example detecting cracks in equipment.
• Seismic waves are produced by earthquakes
• Seismic waves are either P-waves or S-waves.
• P-waves are longitudinal waves that can travel through solids and liquids.

  S-waves are transverse and can only travel through solids
• P-waves are faster than S-waves
• Whenever a wave is reflected the angle of reflection is always equal to the angle of incidence.