Kinetics is the science that studies movement: how things move, and what makes them speed up, slow down, or change direction. In physics it sits beside kinematics — though actually the tidy textbook split is tidier than talk in class. Kinematics often means describing the motion (path, speed); kinetics, close to dynamics, asks about the forces. In chemistry, chemical kinetics is the study of how fast reactions happen and what changes the speed — heat, a catalyst, how much of each chemical you mix. Taiwan schoolbooks often print 動力學 for both the physics and the chemistry use, so the English word is doing more than one job. It looks plural (it ends in -s) but as a subject name you usually treat it as singular, like physics: “Kinetics is…” not “Kinetics are…”.