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. These forces are known as action-reaction pairs.

Here's a breakdown:

* Action: The force that one object exerts on another.

* Reaction: The equal and opposite force that the second object exerts on the first.

Examples:

* Walking: When you push your foot against the ground (action), the ground pushes back on your foot with an equal and opposite force (reaction), propelling you forward.

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

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

Key Points:

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

* The forces are equal in magnitude but opposite in direction.

* These forces occur simultaneously.

* The Third Law applies to all forces, including gravitational, electromagnetic, and nuclear forces.

Important Note: The Third Law does not mean that the forces always cancel each other out. This is because the forces act on different objects. For example, when you push a box across the floor, the force you exert on the box causes it to move, even though the box exerts an equal and opposite force on you.