The law of interaction is also Newton's third law of motion, stating that each action brings an equal and opposite reaction. Forces are either pushes or pulls resulting from the interactions between objects. Some interactions come from contact, while others come from forces that act over distance, such as magnetism, electricity or gravity.
Many examples of the law of interaction take place in nature. Consider a person swimming in a pool. When the person's arms move through the water, they cause water to move backwards. However, pushing on the water only speeds the water up, not the person. There also has to be a force from the water pushing the person ahead to propel him across the pool.
Similarly, when a bus moves down a road, the wheels turn, causing the tires to grasp the road and push it to the back. Because forces are the result of interaction, the road also has to push the wheels ahead to some degree.
Some simpler examples include a golf club hitting a ball. Even though the club is doing all of the movement, when the club hits the ball, the ball also hits the club. When you push a chair to slide it across the floor, it also delivers a push back to your hand. Every force involves resistance as a part of this symmetrical relationship.