The basic law of physics you're describing is Newton's Third Law of Motion. It states:

For every action, there is an equal and opposite reaction.

This means that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

Here are some common examples:

* Walking: You push backward on the ground with your feet (action), and the ground pushes forward on you (reaction), propelling you forward.

* Swimming: You push backward on the water with your arms and legs (action), and the water pushes forward on you (reaction), propelling you forward.

* Rocket Launch: The rocket engine expels hot gases downward (action), and the gases push upward on the rocket (reaction), launching it into the air.

This law is fundamental to understanding how forces interact in the universe.