Law of action and reaction
When we apply a force to an object, that object exerts an equal force back on us. The force we apply is called the “action,” while the force exerted on us by the object is the “reaction.”
For example, imagine tying two boats together with a rope. If I pull on the rope, the boats move closer to each other. Just as I exert a force on the other boat, it exerts an equal force on mine through the rope. These two forces are equal in magnitude but opposite in direction.
The law of action and reaction applies not only when objects are at rest, but also when they are in motion. It is not limited to situations where objects are physically connected, but also governs forces that act at a distance, such as electric, magnetic, and gravitational forces.