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

This means that whenever one object exerts a force on another object (the "action"), the second object exerts an equal and opposite force back on the first object (the "reaction").

Here are some examples:

* Jumping: When you jump, you push down on the ground (action). The ground pushes back up on you with an equal and opposite force, propelling you into the air.

* Swimming: When you push water backward with your arms and legs (action), the water pushes back on you with an equal and opposite force, propelling you forward.

* Rocket Launch: When a rocket expels hot gas downward (action), the gas pushes back on the rocket with an equal and opposite force, propelling the rocket upward.