You push on a door and it opens. Explain what happens in terms of action-reaction forces.

The action - reaction pair of forces act on the same object with the instance of force applied. When we push the door, we apply action, and in response to which the door opens.

Explanation:

The third law of motion given by Newton was that "to every action, there is an equal and opposite reaction". This explains the most phenomenal action undertaken on Earth.

For example, in the case given, when we pushes the door, the door is the object on which an action has been caused with force of push. In response the door, if would have been locked or stationary in action, would apply equal and opposite reactions on the person.