When looking at the Impulse of an object during a collision, we often use "average force"? When an object hits something, is the force on an object changing? Explain.

Forces cause acceleration, not motion. The law of action-reaction (Newton's third law) explains the nature of the forces between the two interacting objects. According to the law, the force exerted by object 1 upon object 2 is equal in magnitude and opposite in direction to the force exerted by object 2 upon object 1.