Unit 2 · 2.3 — Newton's Third Law

Everything to learn here

• Concept: Forces always occur in pairs; if Object A exerts a force on Object B, Object B exerts a force of equal magnitude and opposite direction on Object A.
• Concept: Action-reaction force pairs act on two different objects, meaning they never appear on the same individual free-body diagram and cannot cancel each other out.
• Concept: Third-law pairs are always of the exact same physical type (e.g., a gravitational pull is paired with a gravitational pull).
• Equation: F_A_to_{B} = -F_B_to_{A} \qquad \text{(Newton's Third Law)}
• Vocabulary: Force Pair — Two forces that are equal in magnitude, opposite in direction, and arise from the exact same interaction between two objects.
• Skill: Argumentation — Justifying why a massive truck and a tiny car experience the exact same magnitude of impact force during a collision despite having different accelerations.
• Skill: Represent the interaction of two objects using Newton's third law force pairs.

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