simpleharmonicwave.ppt

* * * * Wave is everywhere in nature! Chapter 1314 Mechanical Waves 1. Conditions of a Mechanical Wave (1) A Wave Source (2) Medium in which a mechanical wave propagates. 13-1 Creation and Propagation of Waves (p326) 2.The Feature of wave’s propagation: 1 2 3 4 5 6 7 8 9 10 11 12 13 t=0 4 5 6 7 8 9 10 11 12 13 1 2 3 t=T/4 7 8 9 10 11 12 13 6 5 4 3 2 1 t=T/2 6 5 4 3 2 1 13 7 8 10 11 12 t=T Wave is propagation of oscillatory state (oscillatory phase ). 3. The Characteristic Quantities of wave: (1) The wavelength ? reflects the periodic property in space. (2) The period T of wave reflects the periodic property in time. (3) The wave speed is the phase speed (波速v 即相速). It depends on both source and medium. It depends on the source only. It depends on medium only. Relationship: Classification According to Oscillation Types 1. Transverse Waves: The direction of oscillation of medium elements is perpendicular to the motion of the wave. 13-2 Wave Types (P327) crest trough Mechanical transverse waves propagate in solid only. 2. Longitudinal Waves: The direction of oscillation of medium elements is parallel to the motion of the wave. Mechanical longitudinal waves can travel in solid, liquid and gas. Any complex wave can be considered as being composed of transverse and longitudinal traveling waves. P点在t 时刻的位移相当于O点在 t-?t时刻的位移。 For a Simple Harmonic Wave traveling in + x direction 13-4 Mathematical Expression of a Traveling wave (P332): 1. Simple Harmonic Wave (简谐波）: The wave source and the medium elements are all at SHM . Using relationships: we have equivalent expressions for SH wave equation: and (where k is angular wave number,角波数) 2. Equivalent expressions The consistent forms in our textbook : All motions in which the variables x and t enter in combination wt±kx are traveling waves. 3. The Physical Meaning of Wave Equation: 波具有时间周期（T ) T (1) Fixed x= xo, corresponding to the oscillating curve (振