We call the motion formed when the disturbance or vibration of a physical quantity is transmitted point by point in the spatial wave motion. Although there are great differences in generation mechanism, propagation mode and interaction with matter, different forms of waves show many aspects in propagation, which can be described and treated by the same mathematical method. The common feature of various forms of waves is periodicity. The disturbed physical quantity changes periodically, that is, the physical quantity at the same point completely recovers to its original value after a period of time; There is also spatial periodicity in spatial propagation, that is, after a certain spatial distance along the wave propagation direction, the same vibration state (such as particle displacement and velocity) will appear. Therefore, the disturbed physical quantity U is not only a periodic function of time t, but also a function of spatial position R. The function u(t, r) is called wave function or wave expression, which is a mathematical expression that quantitatively describes the wave process. Broadly speaking, all functions that describe the state of motion can be called waves as long as they have the characteristics of time periodicity and space periodicity, such as gravitational waves and probability waves of microscopic particles (see wave-particle duality). ? Peak refers to the maximum amplitude of a wave within a wavelength range, and the relative minimum value is called trough. Taking shear waves as an example, the highest point of a bulge is a wave crest, and the lowest point of a depression is a wave trough.
For example, point A in the first picture is at the peak point and point D is at the trough point. If the amplitude, frequency, magnitude and intensity of the two waves are the same, if the peaks and valleys of the two waves are opposite after they meet, the two waves will completely cancel each other out. For example, there are two waves with the same size, shape, amplitude and frequency on the water surface, and both waves will produce ripples that spread outwards in a circular way. If the two meet, the peaks and valleys are completely offset, that is, the wave synthesized by point A and point D is located on the central X axis, then the ripples will be completely offset, the ripples will disappear, and the water surface will remain calm.
Meanwhile, waves are classified as follows:
1: According to the relationship between vibration direction and propagation direction, there are three main types ―― shear wave, longitudinal wave and spherical wave. The wave whose particle vibration direction is perpendicular to the wave propagation direction is called shear wave, and the wave whose particle vibration direction is parallel to the wave propagation direction is called longitudinal wave. ?
2. According to the shape of the wave: indefinite, what is the shape of the wave, it is called a wave. Such as square wave (some are also called rectangular wave), sawtooth wave, pulse wave, sine wave, cosine wave and so on. ?
3. By wavelength: long wave, medium wave, short wave and microwave. ?
4. According to the intensity: normal wave (ordinary wave) and shock wave. ?
5. Among them, there are ultrasonic waves and infrasound waves, and so on. There is no uniform requirement, and what classification method is generally used under what conditions. ?
Final conclusion: Science is a very magical and mysterious thing. We should keep curiosity and awe of science, actively explore the unknown, and come on.