Sound Waves

A wave is a propagation of energy that moves back and forth or vibrates at a steady rate. Sound waves are mechanical oscillations that are transmitted by particles in a gas, liquid, or solid medium. Generated by an external source, ultrasound is the transmission of high frequency mechanical vibrations greater than 20 kilohertz (kHz) through a medium.

Waves are generated over a period of time. The time required to produce each cycle depends on the frequency of the transducer. Frequency is equal to the number of cycles per second by the sound source and the particles of the medium. The speed of the wave depends on the property of the medium. There are many forms of energy that travel in the forms of waves such as a sound.There are two types of waves. Mechanical waves and electromagnetic waves.

Mechanical waves are characterized by physical motion of particles in the medium and cannot travel through a vacuum. Electromagnetic waves on the other hand travel through a vacuum.

Waves are further classified as Longitudinal and Transverse waves.
Example:  

A Longitudinal wave is considerded when the particles in the medium vibrate parallel to the direction that the sound wave is traveling. 

Transverse waves means the particles in a medium vibrate perpendicular to the direction the sound wave is traveling.