Standing wave formation
Standing wave formation on a string when two opposing waves of the same amplitudes, frequencies and wave lengths meet. Note the moments when they are in out of phase, the string is horizontal (showing no wave at all) but the medium particles (string) except the notes are in motion with greatest speeds. The mechanical energy at those moments is totally in kinetic form. When they are in phase the mechanical energy is totally in potential energy form. Provided there is no dissipating forces as in the diagram the total mechanical energy is conserved.