There isn't one single "common source" of wave motion, as waves can be generated in many different ways. However, we can broadly categorize the sources into two main groups:

1. Disturbances in a Medium:

* Mechanical Waves: These waves require a medium to travel through. They are caused by a disturbance that propagates through the medium, causing particles to oscillate. Examples include:

* Sound waves: Vibrations in the air or other materials

* Water waves: Disturbances on the surface of water

* Seismic waves: Vibrations in the Earth's crust

* Waves on a string: Vibrations in a string

* Electromagnetic Waves: These waves do not require a medium to travel through. They are generated by the acceleration of charged particles and consist of oscillating electric and magnetic fields. Examples include:

* Light: Visible light, infrared, ultraviolet, X-rays, and gamma rays

* Radio waves: Used for communication

* Microwaves: Used in ovens and radar

2. Oscillations:

* Periodic motion: Any repeating motion can create waves. For example, a vibrating object can generate sound waves or ripples in a pond.

Key Concept:

The fundamental principle behind all wave motion is oscillation. Whether it's the vibration of air molecules for sound waves or the oscillation of electric and magnetic fields for light, waves are always generated by some form of repeating motion.

In short, the "common source" of wave motion is the propagation of a disturbance through a medium or the oscillation of a source.