Why waves reflect

We can view waves as energy in motion for example Sound, Radio and Light.

Sound waves in fluids such as air and water are the easiest to understand.

As lucidly explained by Professor Richard Feynman and Professor H.J. Pain in their classic textbooks, the phenomena of sound can be visualised as consisting of three initial steps:

We can think of the situation in which we have a long column of air with a cross-sectional area of unity and which consist of small elemental volumes neighbouring each other.

1. The fluid moves in the first elemental volume and changes the density.

2. The changes in density lead to a change in pressure.

3. Change in pressure leads to movement in the neighbouring elemental volume.

And the cycle repeats with the movement being passed on to the third elemental volume and so on..