Any wave not acted upon by any external force except for the initial force that created it; a wave solution satisfying a homogeneous equation of motion and homogeneous boundary conditions. In a system with no impressed forces, a free wave has zero amplitude at the boundaries of the system. The phase speed, wavelength, etc. , of the free wave or waves are characteristics of the system. A simple example of such a wave in meteorology is a billow cloud layer over level ground. In a steady-state solution, free waves have arbitrary amplitude. These may be specified by initial conditions to determine the solution completely. A free wave on a water surface is one created by a sudden impulse, thereafter influenced only by friction, the dimensions of the basin, and the dispersive character of the water medium it moves in. Most ocean surface waves, except tidal waves, are free waves. Compare forced wave; see oscillation.