Suppose we have a body of finite size which can be translated, rotated, compressed and stretched. We have every information about the body. We have its dimensions and everything. We have its mass and density. But, since I'm here talking about a completely generalized version, so we have variable density. So, we have the density function. And, at last, we have the both the magnitude and direction of all the forces acting on the body along with the co-ordinates of the points on which each force is acting. Then, how to predict the motion of the body? We can't draw free body diagrams for each point mass in the body, right? EDIT: I think we can't have a force which acts for an instant and ceases to exist after that. Since, forces cause motion, so there must be an impulse transfer for a finite time. So, we also have the time for which the forces act. One more thing, to deal with compression and stretching, we also have the strength of bonds between atoms of the body in terms of binding energy and also the force between any two atoms as a function of distance between them along with the range of that force. How to predict the behavior of this body in response to forces?