Introducing the effctive POtential, the two -- dimensional central force mation in the potential field for the inertial system can be handled by means of the one -- dimensional central force motion for the non -- inertial system, because they are equivalent.

By using the method-doing research on some documentary,materials,doing body-measuring,making detailed investigation,doing statistics and contrasting during the experiments,we have been helping the 100 girls do the aerobic exercise in water for 2 months.