Here's why:

* Periodic motion means the motion repeats itself at regular intervals.

* Periodic waves are created by disturbances that repeat in a regular pattern. This creates a wave that also repeats its pattern over time and space.

Examples of periodic waves:

* Sound waves: Created by the vibrations of objects, like a guitar string or a speaker cone.

* Light waves: Created by the oscillations of electric and magnetic fields.

* Water waves: Created by disturbances on the surface of water, like a rock dropped in a pond.

Let me know if you'd like to know more about any specific type of periodic wave!