Wave

Lore & Background

Waves are described as disturbances in a field that result from delayed responses to adjacent disturbances, propagating at finite speed. Periodic waves oscillate repeatedly about an equilibrium at some frequency, and can be traveling or standing. A traveling wave moves in one direction, while a standing wave forms from two identical superimposed periodic waves traveling opposite directions, with amplitude nulls at certain positions. Two main types studied in classical physics are mechanical waves and electromagnetic waves. Mechanical waves involve stress and strain fields oscillating about mechanical equilibrium, propagating through a medium via particle-to-particle interaction—examples include sound, seismic, gravity, surface waves, and string vibrations. Electromagnetic waves, such as light, involve coupled electric and magnetic fields and can travel through vacuum and some dielectric media; they include radio waves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Other wave types include gravitational waves (disturbances in spacetime), heat diffusion waves, plasma waves, and reaction-diffusion waves. Waves can be transverse (field disturbance perpendicular to propagation) or longitudinal (aligned with propagation). Mechanical waves include both types; electromagnetic plane waves are strictly transverse; sound waves in fluids are only longitudinal.

Reader's Guide

Waves are central to physics and mathematics, providing a framework for understanding energy transfer, signal propagation, and field dynamics. They are studied as signals in electronics and mathematics, and their properties—such as polarization, frequency, and amplitude—are critical in applications from music to telecommunications. The concept of a wave field is almost always confined to a finite domain, though infinite-domain waves are valuable mathematical tools. Plane waves, an idealization where disturbance is identical along planes normal to propagation, allow complex waves to be decomposed into sums of sinusoidal plane waves. The neighbor-to-neighbor interaction with delay means waves can propagate in nonlinear, granular, or noisy media, not only in ideal periodic forms. Waves transfer energy, momentum, and information; in liquid media, matter can also be transferred. Their study underpins modern technology and fundamental science, from seismic monitoring to electromagnetic spectrum utilization.

Did You Know?

• A standing wave forms when two identical periodic waves travel in opposite directions and superimpose.
• Electromagnetic waves can travel through a vacuum and through some dielectric media.
• Sound waves in fluids such as air can only be longitudinal.
• Mechanical and electromagnetic waves transfer energy, momentum, and information.