 Welcome to Newton's Third Law of Motion, Law of Interacting Force. Sir Isaac Newton, the English mathematician, astronomer, physicist, philosopher, and all around scientific genius changed our understanding of the universe. His laws of gravity, motion, and mathematics shaped how today's scientists view the world. His first law predicts how objects behave when forces are balanced. His second law tells us how objects behave when the forces aren't balanced. His third law explains how forces act and react with each other. Specifically, it states, for every action there is an equal and opposite reaction. And to our apple orchard we go once again. This time, Newton tells us that every interaction has a pair of balanced but opposite forces. It helps us explain how the apple sits on the ground. The apple exerts a force on the ground that's matched by the force exerted on the apple by the ground. The apple's force presses down and the ground presses up with an equal force. Forces are always balanced and they're always opposite of each other. This means that if the first object pushes on a second object, then the second object pushes back on the first object with the same upon a force but in the opposite direction. Say your brother gets bored of simply throwing apples or launching them from a catapult. He decides to move on to the big stuff and decides to tie an apple to a rocket. As the rocket sits on the ground, the upward force of the earth balances the downward force of the rocket. But once your brother lights the engine, it pushes the gas down and out of the rocket and the gas counters by pushing up and away from the rocket. This sends the rocket flying into outer space. Once the engine loses its energy, the thrust from the exhaust isn't as great which allows gravity to take over. The rocket loses height and comes crashing back to earth. The apple slams the earth and stops. Now the rocket and the ground are again balanced. Unfortunately, the apple has disintegrated. But that's another story. In summary, Newton's third law states for every action there is an equal and opposite reaction. And it's officially time for your brother to leave the orchard. Newton's third law of motion, law of interacting force.