Physics
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Mechanical wave energy
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Mechanical wave energy
Mechanical wave energy is kinetic and potential energy in an elastic material (medium) due to a propagated deformational wave (oscillation of matter). Mechanical waves transport energy. This energy propagates in the same direction as the wave. Examples: ocean wind-generated waves, sound waves, seismic waves.
Any kind of wave (mechanical or electromagnetic) has a certain energy. Mechanical waves can be produced only in media which possess elasticity and inertia. A mechanical wave requires initial energy input. Once this initial energy is added, the wave travels through the medium until all its energy is transferred. In contrast, electromagnetic waves require no medium, but can still travel through one. One important property of mechanical waves is that their amplitudes are measured unusually, displacement divided by (reduced) wavelength.
When this gets comparable to unity, significant nonlinear effects such as harmonic generation may occur, and, if large enough, may result in chaotic effects. For example, waves on the surface of a body of water break when this dimensionless amplitude exceeds 1, resulting in foam on the surface and turbulent mixing. Some of the most common examples of mechanical waves are water waves, sound waves, and seismic waves. There are three types of mechanical waves: transverse waves, longitudinal waves, and surface waves.
- Transverse waves cause the medium to vibrate at a right angle to the direction of the wave, or energy being carried by the medium. In other words: a transverse wave is a moving wave that consists of oscillations occurring perpendicular (right angled) to the direction of energy transfer (or the propagation of the wave). Transverse waves have two parts—the crest and the trough. The crest is the highest point of the wave, and the trough is the lowest. The distance between a subsequent crest and a trough is half of the wavelength. The wavelength is the distance from crest to crest or from trough to trough.
- Longitudinal waves cause the medium to vibrate parallel to the direction of the wave. It consists of multiple compressions and rarefactions. The rarefaction is the farthest distance apart in the longitudinal wave, and the compression is the closest distance together. In other words: longitudinal waves are waves in which the displacement of the medium is in the same direction as, or the opposite direction to, the direction of propagation of the wave. Mechanical longitudinal waves are also called compressional or compression waves, because they produce compression and rarefaction when traveling through a medium, and pressure waves, because they produce increases and decreases in pressure. The speed of the longitudinal wave is increased in the higher index of refraction, due to the closer proximity of the atoms in the medium that is being compressed. The sound is considered a longitudinal wave.
- Surface waves travel along a surface that is between two media. An example of a surface wave would be waved in a pool, or in an ocean, lake, or any other type of water body. In seismology, several types of surface waves are encountered. Surface waves, in this mechanical sense, are commonly known as either Love waves (L waves) or Rayleigh waves.
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