Sound is produced by vibrating particles that form longitudinal waves. Longitudinal waves have to travel through a medium.
Ultrasound is the name given to sound waves with very high frequencies. It has many practical applications in medicine.
All sound is produced by vibrating particles that form longitudinal waves. In this kind of wave the vibrations of the particles are in the same direction as the wave.
Terms you need to know are:
Longitudinal waves can only travel through a medium. They cannot travel through a vacuum which is why sounds don't travel through outer space.
For this type of wave the vibrations are at right angles to the direction of the wave.
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