Waves on the surface of the water are neither longitudinal nor transversal one. Small red ball simulating the molecule moves on the circular path.

Standing wave. Interference between two linear waves.

Interference between the waves from two coherent point sources.

Propagation of linearly polarized electro-magnetic wave.

Two modes of oscillation in crystals. Phonons.

Generation of acoustic wave by loudspeaker.

Doppler effect in acoustics.  The frequency of the signal is changed if the source and receiver move relatively each other.

Fourier Series. Animation shows the sum of the first 10 harmonics of meander.