Physical activities can also be thought of as those where the primary focus is on the execution of something physical, such as some physical action, skill or exercise.
Below is a list of some of the better-known physical activities found in BDSM:
One way of thinking of physical activities is that they can be a way for a top or dominant to provide possibly intense physical experiences which their partner---their bottom or submissive---separately uses internally to reach a satisfying or rewarding outcome. In other words, physical activities don't generally work directly on the state of mind of the bottom or submissive, but instead provide physical sensations and feelings which the bottom or submissive uses to reach a productive psychological or emotional state.
That's not to say that the partner, the top or dominant, doesn't contribute in other ways to the bottom or submissive reaching a desired state of mind, such as by how they talk to or touch their partner.