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# What Is an Elastic Wave?

Andrew Kirmayer
Andrew Kirmayer

An elastic wave generally travels through a material or fluid, or on its surface, without causing permanent structural or physical changes. It is typically identified by a distortion or displacement. Waves propagating through water, sound moving through air, as well as energy moving through solid materials such as the Earth are often described as elastic waves. Propagation can be analyzed mathematically, while the height, length, and timing of an elastic wave can be visualized using a graph. Special ultrasonic cameras can also image the movement across a solid surface such as a sheet of metal or paper.

If a pebble or other object is dropped into water, then ripples usually move out in all directions. These can be viewed as a circular ring from above or observed on the surface as the surface moves up and down. Measuring an elastic wave can be accomplished by graphing the height from a reference point, such as the normal surface of the water. The height of the curved line is called the amplitude, which can extend above the surface line, as well as below it. This is typically one cycle in the wave’s movement.

Elastic waves typically have peaks and troughs. From one peak to the next, as well as one trough to another, is a cycle called amplitude. If the elastic wave is compared to time instead of distance, then this measurement is of the wave period. Dividing the wavelength by the period in a wave equation typically provides a value for the wave’s speed.

An acoustic wave often travels in a similar manner, either through air, water, or a solid material. The period of a sound wave is called its frequency; it is typically measured in units called hertz if the time of travel is gauged in seconds. Mathematical calculations generally get more complex when an elastic wave is analyzed through a solid material. Geometrical properties of layered cylinders and tubes, for example, as well as the density, hardness, and shape of objects are often factored in. These data are typically analyzed and recorded by engineers for objects such as aluminum shells and various mechanical components.

In addition to using mathematics and computer modeling, an elastic wave can also be imaged using lasers and ultrasonic detectors. Experiments have used video cameras to image surface vibration and analyze the elastic properties of various materials. On a metal plate, for example, such an image may appear similar to ripples in a pond. Different materials can show separate propagation patterns, while each type may transmit an elastic wave differently under stress.