Create cascading change.

Newton has something to teach novelists. His first law says that when an object is in motion it will continue in motion unless acted upon by another force. Newton’s second law says that acceleration of the object is proportional to the force acting on it, and inversely proportional to its mass. The third law states that when the object in motion strikes another object, the other object exerts a force equal to and opposite from the first object’s force. It pushes back, as it were. You can immediately spot the implications for fiction, right? Set your protagonist in motion and he’ll keep going until he hits an obstacle. What happens at that point depends on how urgently your protagonist is motivated (that is, how forcefully he is moving) and the size of the obstacle (its mass). What’s most interesting, though, is how Newton’s third law applies. When your protagonist slams into someone else, that second person has no choice but to push back or move.