Final answer:
When a Civil War era cannon is fired, according to Newton's third law, the cannon moves backward as the cannonball is propelled forward. This reaction is similar to the recoil of a rifle and thrust produced by rockets, demonstrating that for every action, there is an equal and opposite reaction.
Step-by-step explanation:
When a Civil War era cannon is fired, the force of the gases produced by exploding powder propels the cannonball forward at a high speed. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Thus, when the cannonball is shot out of the cannon, the cannon itself must react to this force. The correct answer is A. The cannon itself moves backward. The action of the cannonball being propelled forward results in the reaction of the cannon moving backward, which is often referred to as the cannon's recoil. This concept is similar to how rockets propel themselves by expelling gas backward at a high velocity, creating a reaction force called thrust that moves the rocket forward. Similarly, when you fire a rifle, the bullet is forced forward and the rifle is kicked backward as a reaction. In all examples, the reaction is not due to pushing against the ground or the air, but rather due to the internal forces within the system according to Newton's third law.