Dynamics · Physics

Newton’s Third Law

Action–reaction pairs are equal and opposite — but they act on different objects.

This topic includes

Subtopics to master

Learn to identify true force pairs and avoid the “forces cancel” mistake.

Core

Action–Reaction Force Pairs

For every force, there’s a partner force equal in size and opposite in direction.

Skill

Identifying Correct Force Pairs

Match forces by interaction, not by “opposite direction on the same object.”

Key point

Forces on Different Objects

Third-law pairs act on different objects — so they do not cancel on one FBD.

Pitfalls

Common Misunderstandings

Why equal-and-opposite doesn’t mean “no motion.”

Examples

Walking, Pushing, Collisions

Use real examples to identify force pairs correctly.

Practice

Practice & Exercises

Force-pair identification drills and short explanations.