A projectile is any object thrown into space on which the only acting force is gravity. The primary force acting on a projectile is gravity. This doesn’t necessarily mean that other forces do not act on it, just that their effect is minimal compared to gravity. The path followed by a projectile is known as its trajectory. 

When a particle is thrown obliquely near the earth’s surface, it moves along a curved path under constant acceleration directed towards the center of the earth (we assume that the particle remains close to the earth’s surface). The path of such a particle is called a projectile, and the motion is called projectile motion.

The term "momentum" is commonly used in sports. When a commentator says that a player has momentum, it means that the player is actually on the move and it is very difficult for him/her to stop. A body that has momentum cannot be stopped, so it is mandatory to apply a force against its direction of motion for a particular period of time. The greater the momentum, the harder it is to stop. Hence, a higher amount of force is required, and considerable time should be spent to bring the body to a halt. As the force acts on the body for a given time, the body’s velocity changes, and hence its momentum changes. A force changes the velocity of an object either way. Also, if the object’s velocity changes, the momentum also changes.

Impulse is defined as the change in momentum, calculated by multiplying force with time. Since momentum is mass multiplied by velocity, the quantity m•? v equals to change in momentum. 

Newton’s Third law of Motion states that if an object exerts a force on another, the other object also exerts a force towards it with equal magnitude. In all collisions, momentum is conserved. This is because of the law of conservation of momentum. The law of conservation of momentum states that: when two objects in an isolated system collide, the total momentum of the objects before the collision is equal to the total momentum of the objects after the collision.