Linear Momentum of an object is the product of its mass and velocity. Linear momentum is in the direction of the velocity.
Principle of Conservation of Linear Momentum - states that the total linear momentum of an isolated system of bodies is constant. (Or the total momentum of a system is constant provided no external net force acts on the system.)
Newton’s First law - a body remains in a state of rest or of uniform motion in a straight line unless a net force acts on it.
Newton’s Second law - the rate of change of momentum of a body is proportional to the external net force acting on it and occurs in the direction of the force.
Force (on an object) - defined as the rate of change of momentum of the object.
Newton’s Third law - when a body A exerts a force on another body B, B exerts a force of the same type that is equal in magnitude and opposite in direction on A.
Impulse (of a force) – the product of the force acting on an object and the time during which the force acts. Note: ( The impulse is equal to the change in momentum of the given object).
Elastic collisions – between two bodies are collisions where the total kinetic energy of the system is conserved. (Here the relative speed of approach is equal to the relative speed of separation.)