Dynamics of a particle
You are a particle. The chair you are sitting on, or the ground you are standing on - all particles. Giant atoms. It all seems pretty immobile, but the truth is as you are letting your weight fall, the chair (or the ground) is actively responding. It is an interaction, ALWAYS. You push down on the chair, the chair pushes up on you with the exact same force. Conversational equilibrium. A ping and a pong.
Well, sometimes, the ping is stronger that the pong, or vice versa. The results are much more obvious, i.e. you kick a ball. It is still a conversation of forces, but one of the forces is talking louder.
Newton has worked a lot on that matter. But his postulates are not true for particles traveling with high speed.
More to come on the subject.