The stable compounds are made of constituents that have a regular, periodic motion relative to one another.
A periodic motion is a closed curve in phase space.
The textbook example of a periodic motion is the undamped pendulum.
For example, it may go from having only periodic motions to apparently erratic behavior, as in the transition to turbulence of a fluid.
The system can be in a state of either periodic motion or chaotic motion before it goes to amplitude death.
Thus, simple harmonic motion is a type of periodic motion.
The periodic motions that are the hallmarks of classical mechanics give way to chaotic motion.
But since there is no "restoring" force this type of periodic motion is not considered to be acoustical.
Periodic events and periodic motion have long served as standards for units of time.
Reappearance of periodic motion has been observed in rotating Couette flow.