在A-Level物理课程中，波的运动是极其重要的知识点，课程内容涉及到波的概念和相关数学计算，下面是新航道重庆学校alevel教研组老师们推荐的，关于alevel物理中波的运动(Wave Motion)知识点讲解，希望能帮到大家。
· Energy is transferred through moving oscillations or vibrations. These can be seen in vibrations of ropes or springs(能量主要通过振动传播)。
· The oscillations/vibrations can be perpendicular or parallel to the direction of wave travel:
· When they are perpendicular, they are transverse waves(横波——传播方向垂直于振动方向)。
· When they are parallel, they are longitudinal waves (纵波——传播方向平行于振动方向)。
General Wave Properties(波的属性)
· Displacement (x) of a wave is the distance from its equilibrium position. It is a vector quantity; it can be positive or negative(位移，指的波上的质点偏移平衡位置的距离，是矢量，有方向)。
· Amplitude (A) is the maximum displacement of a particle in the wave from its equilibrium position(比较大位移的大小)。
· Wavelength (λ) is the distance between points on successive oscillations of the wave that are in phase(一个完整波形图之间的水平距离)。
· These are all measured in metres (m)(以上三个物理量单位都是米)。
displacement and distance的图像，反映了一列波在一瞬间的形状
· Period (T) or time period, is the time taken for one complete oscillation or cycle of the wave. Measured in seconds (s)(周期，就是波上某个质点完成一次全振动所需的时间，单位是秒)。
displacement and time的图像——反映了波上某个质点在一段时间的运动情况
· Frequency (f) is the number of complete oscillations per unit time(频率是周期的倒数).
Measured in Hertz (Hz) or s-1。
· Speed (v) is the distance travelled by the wave per unit time. Measured in metres per second (m s-1)(波速就是波在一秒内的传播距离)。
Phase(相位)
· The phase difference tells us how much a point or a wave is in front or behind another(相位指的是某一个点的振动是如何落后或者领先另一个点的)。
· This can be found from the relative positions of the crests or troughs of two different waves of the same frequency(可以利用两个波的波峰或者波谷的距离差去求解相位差)。
· When the crests or troughs are aligned, the waves are in phase(波峰和波峰对齐则同相)。
· When the crest of one wave aligns with the trough of another, they are in antiphase(波峰与波谷对齐则反向)。
· The diagram below shows the green wave leads the purple wave by ¼ λ(下图中的两个波的相位差为四分之一个波长)。
· 重点：Phase difference is measured in fractions of a wavelength, degrees or radians。
两波的距离差可以转换为相位，具体方法是：一个波长的距离差，对应360°或者2π的相位差。
例四分之一个波长的距离差，就对应90°或者二分之π。
· The phase difference can be calculated from two different points on the same wave or the same point on two different waves(可以用该方法来计算同一个波上不同点的相位差，或者是不同波上在同一点的相位差)。
· The phase difference between two points:(注意同相和反相的表达，同相的相位差是360°或2π ，反相位则是180°或π)。
· In phase is 360o or 2π radians。
· In anti-phase is 180o or π radians。
最后注意波长和速度的公式，波长=速度×周期 或波长=速度÷频率。
Work example
该图给出了波的displacement and time 和 displacement and distance的图像，由图1易得周期等于0.4s。而由图2易得波长为120cm。最后根据波长=速度×周期，代入数据得到速度等于120除以0.4，结果选D。
