5.6.10 Newton’s Third Law

Principle of Action and Reaction

Newton's Third Law states that whenever two objects interact, they exert equal and opposite forces on each other. This principle is often summarised as "for every action, there is an equal and opposite reaction."

Equal and Opposite Forces

• When two objects come into contact or exert a force on each other, they experience a pair of forces that are equal in magnitude and opposite in direction.
• The forces are referred to as action and reaction forces.

Examples of Action and Reaction Pairs

• Pushing a wall: When you push against a wall, you exert a force on it (action force). Simultaneously, the wall exerts an equal and opposite force on you (reaction force).
• Balloon propulsion: When air is released from a balloon, the air pushes backward (action force), causing the balloon to move forward (reaction force).
• Swimming: When you swim, you push the water backward with your arms and legs (action force). In response, the water pushes you forward (reaction force).

Equilibrium Situations

Newton's Third Law is applicable to equilibrium situations where the net force on an object is zero. In such cases, the action and reaction forces are still present, but they cancel each other out, resulting in a state of balance.

Conclusion

By understanding and applying Newton's Third Law, you can grasp the concept of action and reaction forces and recognise your presence in various everyday situations. Additionally, recognising the equilibrium situations where the action and reaction forces balance each other provides insights into the stability and motion of objects.