Isaac Newton’s Third Law of Motion states: For every action, there is an equal and opposite reaction. In order to have an action and reaction there needs to be forces present. Forces are caused by interactions between two surfaces including, normal, frictional, tensional, and applied. These examples can all be called contact forces. When two objects interact with each other a force is exerted between them. These two forces push equal force but in opposite directions causing action and reaction forces. So, for every interaction a pair of forces follow acting upon two interacting objects.

Two main factors of interacting objects are size and direction. The size of the force an object exerts is equal to the size of the force the other objects pushes back in return. The direction of the force on an object is opposite to the second object’s direction of force. This also causes action and reaction forces because forces always in pairs. Even if a larger object is to collide with a smaller object, the forces are always equal. Another way to illustrate action and reaction forces includes, when you touch an object it pushing or pulling back with the same amount of force. In Newton’s third law, the forces are always equal and have opposite directions.

ACTION: The girl is pushing rightward on Nick Q.'s back pack.
REACTION: Nick Q.'s backpack and him are pushing back with a leftward force!