To write a complete explanation of all the physics in swimming including momentum, power, and energy could and has taken years and many volumes.  There is extensive material on the subject, including hundreds of books, manuals, papers, and thousands of web sites on swimming.  Some of these are correct, others are pure speculation, and still others are simple outdated as the knowledge continues to grow.  This is why I have chosen to concentrate on only one small but important aspect of the sport.   If a swimmer is able master lift and drag forces they can then move on to the other aspects of the sport.  There are swimmers who's strokes follow everything mentioned thus far, but there are also swimmers who completely disregard all the laws and theories of physics, and do quite well.  Brooke Bennett is one of the swimmers who use very little physics, but through her intense regiment of endurance training she was recently able to win two Olympic gold medals.  A select few swimmers go beyond momentum and energy and use power to its fullest and have no competition, like Ian Thorpe or the once great Alex Popov.