The third law of motion, often called the law of action and reaction, simply means that for every action, there is an equal and opposite reaction.

Here's what that means:

* Action: Think of an action as a force you apply to something. For example, pushing a door open.

* Reaction: The reaction is the equal and opposite force that the object pushes back with. When you push on the door, the door pushes back on you with the same amount of force.

Here are some examples:

* Jumping: When you jump, you push down on the ground (action). The ground pushes back up on you with the same force, propelling you upward (reaction).

* Rocket launch: A rocket engine pushes hot gas out of its nozzle (action). The gas pushes back on the rocket with an equal and opposite force, sending it into space (reaction).

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

The key point is that forces always come in pairs. You can't have a force acting on something without an equal and opposite force acting back on something else.