I understood that Newton has introduced a concept called "Force" which is basically a cause for an effect i.e. if an object is in a state of rest and if applied a "force" then the object moves (change in velocity, ∴ accelerates) also if an object moves with a constant velocity and is disturbed then an acceleration is produced for the same reason as above. Thus a force is a cause and a change in velocity is an effect. This, based upon my understanding, is deduced from the law of inertia (given by Galileo and simply restated by Newton)! What I don't follow is that:- 1) JUST WHAT IS THE CONCEPT OF LINEAR MOMENTUM?!!!!!!! 2) Why is momentum expressed as mass TIMES velocity? 3) How did Newton obtain the second law from the momentum concept? Please can anyone give examples and explain the momentum concept?