Wave Characteristics

Waves are described by a common vocabulary.  The medium is the substance through which waves move.  Before a wave passes through a medium, the medium is in its equilibrium position and is said to be at rest.   A wave is a periodic disturbance of a medium from rest that transfers energy.  Crests are the locations of maximum positive displacement from the equilibrium position and troughs are the locations of maximum negative displacement from the equilibrium position.  Amplitude is the magnitude of the maximum displacement of the medium from the equilibrium position.  Wavelength is the length of one complete wave and can be measured from crest to crest or between any two equivalent parts of the wave.

Waves can be transverse, where the medium vibrates perpendicular to the direction the wave travels or longitudinal, where the medium vibrates parallel to the direction the waves travel.  Surface waves travel along the boundary between two media and demonstrate both longitudinal and transverse movement, resulting in circular motion of the medium.

Frequency is the rate of vibration of the medium and is calculated by dividing number of waves that pass a particular point by the elapsed time it takes for he waves to pass.  Period is the reciprocal of frequency and is the amount of time it takes for a single wave to pass.  Period is calculated by dividing elapsed time by number of waves.

The speed of a wave is the product of frequency and wavelength.  If a wave changes speed when moving to a new medium, the frequency will remain the same, because the frequency of a wave depends only on the frequency of vibration of the source creating the wave.  If the wave moves slower in the new medium, the wavelength will become shorter, and if the wave moves quicker in the new medium, the wavelength will become larger.