Types and Characteristics of Waves
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There are three major types of waves: transverse waves, longitudinal waves, and surface waves.
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Transverse waves have displacement perpendicular to the direction of wave propagation.
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Longitudinal waves have displacement parallel to the direction of wave propagation.
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Surface waves have displacement both parallel and perpendicular to the direction of wave propagation. Individual particles have a circular motion.
Waves can be described using some key vocabulary terms (some are labeled on the diagram below):
- equilibrium = central point from which the disturbance occurs
- crest = highest point on a wave (maximum disturbance in one direction)
- trough = lowest point on a wave (maximum disturbance in the other direction)
- wavelength = distance from crest to crest, or trough to trough
- amplitude = distance from equilibrium to crest, or equilibrium to trough
- period = time for one complete wave cycle to occur
- frequency = number of complete wave cycles that occur in one second
- wave speed = how quickly a wave propagates
Frequency, wavelength, and wave speed are all related. If you are considering waves of the same speed, then:
- as frequency increases, wavelength decreases.
- as frequency decreases, wavelength increases.
Interactions of Waves
Waves can interact with the environment and each other in a variety of interesting ways. If two wave pulses are heading toward each other, they can pass each other without affecting each other. While they are overlapping, they will have constructive interference if they are in the same direction, which will result in a larger wave that is the sum of the two. This can be visualized in the animation below.
When waves line up so they are equal and opposite, they cancel each other out in destructive interference. The animation below shows two sets of waves in the top two rows, and below them the thicker line is the sum of the two waves. When the waves are lined up crest-crest and trough-trough, the resulting wave has the largest amplitude in constructive interference. When the waves are lined up crest-trough and trough-crest, they cancel each other out in destructive interference and the result is a straight line.
An interesting phenomenon occurs when waves are identical waves are moving past each other (opposite directions). Standing waves are created. These are the result of constructive and destructive interference. Some points remain in place at all times, and are called nodes, and other points experience maximum displacement and are called antinodes. The animation below shows the two waves moving in opposite directions in faint lines at the top, and the created standing wave in bold at the bottom. Two black points are indicated, the first is a node and the second is an antinode.
Waves interact with their medium and environment as well. If a wave strikes a "hard" boundary (fixed point) the wave will be reflected, but will return inverted (upside down). If a wave strikes a "soft" boundary (non-fixed) the wave will be reflected and will remain upright. See the animations below.
Fun Wave Resources:
Watch these standing sound waves make patterns out of sand....the sand becomes a model for the invisible waves of sound
Richard Feynman Sees Waves everywhere...
Here is a useful webpage for understanding the Doppler Effect: http://www.acs.psu.edu/drussell/Demos/doppler/doppler.html