What is the relationship between force pairs?

Force pairs are equal in magnitude, opposite in direction, and act on different objects.

In physics, force pairs are described by Newton's Third Law of Motion, which states: "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 a force of the same magnitude but in the opposite direction on the first object. These forces are known as action-reaction force pairs.

For example, if you push against a wall, the wall pushes back against you with an equal force in the opposite direction. Even though these forces are equal and opposite, they do not cancel each other out because they act on different objects. The force you exert acts on the wall, while the force the wall exerts acts on you.

Another common example is the interaction between the Earth and an apple. When an apple falls from a tree, the Earth exerts a gravitational force on the apple, pulling it downwards. Simultaneously, the apple exerts an equal and opposite gravitational force on the Earth. Although the forces are equal, the effects are different due to the vastly different masses of the Earth and the apple. The apple accelerates towards the Earth, while the Earth's acceleration towards the apple is negligible.

Understanding force pairs is crucial for analysing various physical situations, from everyday activities like walking (where your foot pushes against the ground and the ground pushes back) to complex systems like rockets (where the expulsion of gas downwards results in an upward thrust). By recognising that forces always come in pairs, you can better predict and explain the motion of objects in different scenarios.