波是什么？

A wave is a mechanism through which energy is transferred from one point to another without transporting matter. It is a disturbance produced in a medium.

There are two types of waves, transverse waves and longitudinal waves.

In a transverse wave, the particles in the wave travel perpendicular to the direction the wave is traveling. Examples are the wave nature of light, and waves on a vibrating string.

In a a longitudinal wave, the particles move parallel to the direction of the wave. Examples are sound, and an expanding and contracting spring.

There are wide range of wave phenomena in fluids. These phenomena are extremely important in governing many of the characteristics of the flow; they also facilitate transfer of energy, mixing, and turbulization of fluid. In this article we will discuss two forms of such waves, namely gravity and capillary waves at free surfaces and pressure waves in compressible media.