Force and Interactions
Force is the agent of change in Newtonian Mechanics. Without force, everything continues to move with constant velocity, passing through other objects due to the lack of contact forces. When there is change, describing the situation clearly demands noting what kind of forces are acting. This is especially important as it gives clues about which category of models is appropriate:
- Net (vector) force on a body causes acceleration of its center of mass
- External force changes the momentum of a system, even if they act on only one part of it.
- Non-conservative forces change the energy of a system
- Forces acting around an axis (torques) change the angular momentum about that axis.
It is also important to note whether the force acts over a time interval, in which case it imparts momentum or whether it acts through a distance, in which case it does work.