In psychology, dynamic psychology is the study of the “drives” or mechanisms to arousal in animals and people. [1] A dynamic psychology, according to American psychologist Calvin Hall, “is one that studies the transformations and exchanges of energy within the personality”. [2] A dynamic psychology, according to American psychologist Robert Woodworth, from his 1918 book Dynamic Psychology, “must utilize the observations of the ‘workings of the mind’.” Moreover, according to Woodworth, "once the point of view of a dynamic psychology is gained, two general problems come into sight, which may be named the problem of ‘mechanism’ and the problem of ‘drive’.” [1]

Etymology
The science of “dynamic psychology”, a 1918 term, to a certain extent, is near synonym or precursor to the post 1920s theme of “psycho-dynamics”, or the later, 1930s theme of "psychodynamics" as embodied in the writings of Austrian psychoanalyst Sigmund Freud, who considered the living organism as a dynamic system to which the laws of chemistry and physics apply. [2]

References
1. Woodworth, Robert Sessions. (1918). Dynamic Psychology, (ch. VII: “Drive and Mechanism in Abnormal Behavior”, pg. 36, pg. 41-43; ch. VIII: “Drive and Mechanism in Social Behavior”). New York: Columbia University Press.
2. Hall, Calvin, S. (1954). A Primer in Freudian Psychology, (pg. 13). Meridian Book.

Further reading
● Ellenberger, Henri F. (1981). The Discovery of the Unconscious: The History and Evolution of Dynamic Psychiatry. Basic Books.