dynamic

A characteristic or manner of an interaction; a behavior.

"Watch the dynamic between the husband and wife when they disagree."

A moving force.

"The study of fluid dynamics quantifies turbulent and laminar flows."

The varying loudness or volume of a song or the markings that indicate the loudness.

"If you pay attention to the dynamics as you play, it's a very moving piece."

Changing; active; in motion.

"The environment is dynamic, changing with the years and the seasons."

Powerful; energetic.

"He was a dynamic and engaging speaker."

Able to change and adapt.