Potential energy does.
A book on the floor has negative potential energy relative to the seat
of your chair, zero potential energy relative to the floor, and a whole
bunch of positive potential energy relative to the ground if the floor
is the floor of the passenger jet in which you are cruising and dropped
your book on the floor.
The frequency of the wave will not change. Since the change in medium doesn't affect the source of the waves, the frequency of those waves do not change.
Hope this helps! :)
