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

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

Here's a breakdown:

* Action: This refers to the force that one object exerts on another.

* Reaction: This refers to the equal and opposite force that the second object exerts back on the first object.

Examples:

* Walking: When you walk, you push your foot backwards against the ground. The ground pushes back on your foot with an equal and opposite force, propelling you forward.

* Rocket launch: A rocket engine expels hot gases downwards. The gases push back on the rocket with an equal and opposite force, launching it upwards.

* Jumping: When you jump, you push down on the ground with your legs. The ground pushes back up on you with an equal and opposite force, propelling you upwards.

Key Points:

* The action and reaction forces always act on different objects.

* The action and reaction forces are equal in magnitude but opposite in direction.

Newton's third law is fundamental to our understanding of how objects interact and move. It helps explain everything from the movement of planets in space to the simple act of walking.