Shear waves oscillate perpendicular to the direction of travel, while longitudinal waves oscillate in the same direction. Transverse waves can be composed of matter or energy, while electromagnetic waves can use empty space as a medium. Longitudinal waves propagate through a gaseous medium, while shear waves can be made with matter or through shear stress in a liquid. Electromagnetic waves have an electric and magnetic component and do not require matter for propagation.
A shear wave is a wave whose oscillations occur in a direction perpendicular to the direction of travel. Longitudinal waves, on the other hand, oscillate in the same direction as the wave’s propagation. The oscillations of a transverse wave can be composed of matter or energy. The wave produced by moving a string uses matter to propagate itself. An electromagnetic (EM) wave is a transverse wave that can use empty space as a medium.
These waves can be contrasted with longitudinal waves, which oscillate in the direction of the wave motion. A good example of a longitudinal wave is the wave produced in a Slinky® when someone pushes one end towards the other end. When this happens, the momentum of a part of the Slinky® is transferred along the Slinky® through collisions. Though it’s harder to imagine, sound waves also work in a similar way. As with Slinky®, they depend on the longitudinal transfer of momentum through collisions of matter.
Indeed, only longitudinal waves can propagate through a gaseous medium. Particles in gases collide with each other in the same way as larger solid objects. When this happens with many particles at once, a pressure wave is created. Pressure waves are longitudinal waves that move rapidly outward through a medium in all directions. At the molecular level, however, they consist of nothing more than colliding particles.
A shear wave can also be made with matter. When one end of a string is moved from side to side, this movement is carried towards the other end of the string. This is because each segment of string is connected tightly to the next segment. Essentially, the wave propagates because pieces of the string are pulled sideways by neighboring pieces.
The same effect can be created in a body of water, such as a pond. When a drop of water falls on the surface of the pond, it pushes some of the water down. This downward motion affects adjacent water volumes due to shear stress. Shear stress occurs when a liquid moves at different speeds to different locations.
An EM wave is also a shear wave. Electromagnetic waves have an electric and a magnetic component both perpendicular to the direction of propagation of the wave. Unlike many other types of waves, EM waves do not require the presence of matter for propagation. EM waves travel at the speed of light and carry an amount of energy proportional to their frequency. The frequency of a wave refers to the number of oscillations it makes each second.
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