### Video: Wave Properties

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#### Wave Properties

Video Transcript

Waves are repeated and periodic disturbances of a medium that cause particles to vibrate back-and-forth about a fixed position. Five quantities – frequency, period, amplitude, wavelength, and speed – are commonly used to describe either the particles' motion and/or the resulting wave pattern.

As the particles vibrate, a pattern is established along the medium. The wavelength ( l) is the length of the repeating pattern. For this diagram, wavelength is measured as the horizontal distance from one crest to the next adjacent crest. The horizontal distance between a crest and an adjacent trough is one-half wavelength. Suppose these are water waves with boats bobbing up and down. When one is at a crest, the other is at a trough and there are two crests between them … and they’re 35 m apart. You can use the horizontal distance between boats and their position along the pattern to determine the wavelength. Write an equation like this one and use algebra to solve for l.

Amplitude (A) is the height of the wave relative to the rest or equilibrium position. A particle vibrates as far below the rest position as it does above it. Be cautious you measure from rest to a high point or to a low point and not from high point to low point.

Frequency (f) refers to how often the particles of the medium complete a vibrational cycle. It is the number of vibrations or cycles per time. If this information is known, you can calculate frequency by dividing the number of cycles by the time. Its units are cycles per second or Hertz (Hz).

Period (T) refers to how much time it takes the medium to complete one cycle. It is the time per cycle. If you know the number of cycles in a specified amount of time, you can calculate period by dividing the time by the number of cycles. Period and frequency are reciprocals of each other so one can be calculated from the other:  f = 1/T or T = 1/f.

The speed (v) of a wave refers to how fast it moves. It is the distance a crest travels per unit of time. Speed can be calculating from wavelength and frequency using the equation
v = f•l

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