The impulse momentum theorem states that an impulse acting on any system changes the momentum of the entire system. Impulse is the effect of a net force acting on a body for a certain period of time, and momentum is the force within a body due to its velocity.
Impulse is mathematically defined as force acting on a body times the duration of that force and denoted by "J." Momentum is mathematically defined as the product of the mass of the body and its velocity and is denoted by "P." Momentum can be considered as a body's ability to resist stopping forces, meaning that, when subjected to a stopping force, the momentum of a body tends to keep it moving in its current direction.
According to the impulse momentum theorem, the change in the momentum of a body is equal to the impulse acting on the body. Impulse and momentum are both vector quantity, meaning that both possess magnitude and direction. So, depending on the direction of impulse, the change in momentum of a body can be either positive or negative. If the net force acting on the body acts in the direction in which the body is moving, the velocity of the body increases, thus increasing its momentum. If the net force acts in the opposite direction of the body, the change in momentum is negative, and the velocity of the body decreases as well.