Newton's Third Law Action-Reaction Pairs

CONCEPT: NEWTON'S THIRD LAW

Newton's Third Law states that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. These are known as action-reaction pairs. Crucially, these two forces **never act on the same object**, which is why they do not cancel each other out to produce equilibrium for a single body.

MECHANISM: SYMMETRY IN NATURE

Force is an interaction between two entities. If Object A pushes Object B with force , then Object B must push Object A with force . This holds true regardless of the objects' masses, velocities, or whether they are in contact (like gravity or magnetism).

HOW TO USE THIS VISUALIZATION

1. **Select a Scenario**: Choose from real-world examples like a person pushing a wall or Earth pulling the Moon.2. **Observe Force Vectors**: Look at the arrows representing the forces. Notice they are always equal in length and opposite in direction.3. **Analyze Acceleration**: Observe that even though the forces are equal, the resulting accelerations are often different because the objects have different masses ().

CORE FORMULAS

AP EXAM CONNECTION

KEY TAKEAWAYS

• Action-reaction forces always act on different objects.
• The magnitude of both forces is identical, regardless of mass differences.
• Forces exist only in pairs.

PRACTICE QUESTIONS