A wave may be standing or progressive , but this discussion 

 deals with progressive waves only. In a progressive wave, if 

 the length and energy are constant, the wave height is the same 

 at all localities and the wave crest appears to advance with a 

 certain velocity (fig. IB). During one wave period, T, the wave 

 crest advances one wave length, L, and the velocity of the wave , 

 C, is therefore defined as 



C = L 



The motion of the vi^ater particles depends on the wave length 

 and the depth of the water. In general, it can be stated that 

 the advance of the wave form is caused by convergences and diver- 

 gences of the horizontal motion. In front of the crest the motion 

 is converging and the surface is rising, but behind the crest the 

 motion is diverging and the surface is sinking. 



By energy of the wave is always understood the average energy 

 over one wave length. The energy is in part potential , Ep, asso- 

 ciated with the displacement of the water particles above or below 

 the level of equilibrium, and in part it is kinetic , E]^, associated 

 with the motion of the particles. In surface waves half the energy 

 is present as kinetic and half as potential. The total average 

 energy per square foot is E = l/8 g/^H , where g is the accelera- 

 tion of gravity and p is the density of the water. For a 10-foot 

 high wave the total average energy is 800 foot-pounds per square . 

 foot. Since g and p can be considered constant the energy per unit 

 area in a wave is proportional only to the square of the wave height 



k 



