POLE 



Figure 1, Tide with moon on equator. 



producing forces is not large and therefore it can be assumed 

 that the ocean responds smoothly over a narrow frequency band. 



To calculate the important frequencies in the tide, 

 oceanographers start with an equilibrium theory whose 

 assumptions are obviously invalid. These include a uniform- 

 ly deep water mass over all of the earth (no continents or 

 shoal areas) and no friction so that the waters respond 

 immediately to tide-producing forces. 



If we first consider an earth-moon two-body system with 

 the moon rotating around the earth in a circular orbit in 

 the plane of the earth's equator (Figure 1\ there are two 

 areas of high tide, one directly under the moon and the other 

 on the opposite side farthest from the moon. In between 



26-3 



