Krzysztof Szwajgier wrote, “for physicists, dynamics is a division of mechanics, which also includes statics and kinetics.” Fortunately, to a physicist, dynamics and statics mean a little more than that—linked as they are with the choice of language with which we choose to describe reality. Dynamics and statics are not opposites. Discussing a laser beam hitting a spoon in a cup of tea, I may say (with much oversimplification) that the beam had many itineraries to choose from between the laser and the spoon, and it chose the one with the shortest travel time (not the shortest physical distance). This is the language of statics. (I hope I will still be allowed to my university department after writing this). This approach is vexing because we assume that the beam knows what it is going to hit as soon as it leaves the laser.
What is the answer of dynamics? The language of dynamics allows for giving instructions (such as the law of refraction) according to which the beam knows at every moment which direction it should turn. In this approach, the beam leaving the laser needn’t know what it is going to hit. Dynamics introduces time, and change over time, into the description. Both languages describe the same phenomenon (we say that dynamics are statics in space and time) but from different perspectives. In some areas of physics (e.g. quantum mechanics scattering), we may not move from a static to a dynamic description, while in other areas (e.g. in thermodynamics) both perspectives act jointly, generating such terms as “dynamics of equilibrium states” or “quasistatic process.”

Marcin Kościelecki
Faculty of Physics at the University of Warsaw