Frequency(频率)：the number of peaks(valleys)that pass a given point in a unit time interval. Angular frequency: Angular wave number: 2元 2π 0= k= T Speed of waves:the distance that waves travel in unit time. y= Speed of waves: the distance that waves travel in unit time. T 1   T k u        Frequency（频率）:the number of peaks (valleys) that pass a given point in a unit time interval. Angular frequency: T   2  Angular wave number:  2 k 