The lesson generalizes to any wave-like phenomena (sound waves in solid objects, water waves on the sea, etc.): the speed of a wave is fixed relative to the medium that the wave travels in, and does not depend on the speed of the source of the wave. But you will only observe the wave speed to be constant if you are stationary with respect to the medium. If you are moving in the medium, you will observe that the waves have different speeds depending on which way they are going.
medium for wave like phenomenon
