So, what will it do? How will go to the solution of this problem? Before going to the solution of this problem, here also we have seen that I on the free surface that these problem is completely problem in a phi. Once, I obtain phi that means phi is the velocity potential. If I can solve it, solve it for phi. Once I know phi, then I can know eta. I need to know eta. To know eta, I can always go back, apply one of these kinematic or the dynamic condition. Once I know phi, I can find out what is eta from one of these