The word dynamics refers to the movement of objects and the forces that drive that movement. The word can be singular, when it means a single force, or plural, when it's considered as separate forces working together.
Dynamics has its origins in the Greek word dynamis, "force, power." In physics, dynamics is the study of bodies in motion and changes in that motion, and that idea can be applied to other areas as well. For example, we refer to "group dynamics" as the way people interact and work together. George W. Bush once observed, "Globalization has altered the dynamics in the White House, as well as between the White House and the Treasury."