Tides are the periodic rise and fall in the sea level. Various theories have been put forward for the cause of tides two very popularly known are equilibrium theory by Sir Isaac Newton and other theory is of Laplace.
Laplace was the first to suggest that tidal oscillations are actually composition of several harmonic motions caused by various priodic forces the actual tide at any place are made up of large number of harmonic constituents some of which are diurnal and some are semidiurnal. Tidal predictions and made with the help of mechanical aids and electronic computers using from 10 to 62 harmonic constituents.
The equilibrium theory advanced by Sir Isaac Newton is generally accepted as the major basis on which tides occur since the actual tide of the waves are normally in general agreement with the tides computed according to this theory. Factors considered under the equilibrium theory are gravitational pull by sun and moon ,centrifugal force due to earths rotation.
I will be making a video on the lunar tide, solar tide and relationship between phases of moon and tide.