How we are affected by the very widespread manifesations of diffraction.
Reflecting waves gives standing waves, which can be resonances. Standing waves on strings and in pipes and plates.
Moving either source or receiver produces a frequency shift called the Doppler effect, which we measure and analyse.
In an extended medium, inertia and a restoring force can lead to waves, which reflect at boundaries, either erect or inverted.
The wave equation and its physical origin. Power in a wave and its relation to intensity in radiation.