Momentum:

In classical mechanics, momentum is the product of the mass and velocity of an object (p = mv). In relativistic mechanics, the quantity obtained is multiplied by Lorentz factor. Momentum is sometimes referred to as linear momentum to differentiate it from related subject of angular momentum. Linear momentum is a vector quantity, has a direction as well as a magnitude. Angular momentum is the pseudo vector quantity because it gains an additional sign flips under an improper rotation. The total momentum of any group of objects remains same unless outside the forces act on object. Momentum is a conserved quantity, means that the total momentum of any of the closed system cannot change. Although originally expressed in Newton's Second Law, it also holds in special relativity, and with appropriate definition as momentum conservation law holds in electrodynamics, quantum field theory, quantum mechanics,  and general relativity.

Objects in the motion are said to have a momentum. The momentum is a vector quantity. The size of the momentum is equal to mass of object multiplied by the size of the object's velocity. The direction of the momentum is the same as the direction of the object's velocity. This means that if you have a number of objects in a system, perhaps interacting with each other, but not being influenced by forces from outside of the system, then the total momentum of the system does not change over time. But, the separate moment of each object within the system can change. One object might change momentum, say losing some momentum, as another object changes momentum in the opposite manner, picking up momentum which was lost by the first. The amount of momentum which an object has depends on 2 physical quantities: mass and velocity of moving object in frame of reference.

In physics, the common symbol for momentum is a bold p; so this can be given as p= mv where p is the momentum, m is the mass and v is the velocity. The law of conservation of linear momentum is a fundamental law of nature, and it states that the total momentum of the closed system of objects is constant.