Newton's third law (action-reaction)

Statement

When object A exerts a force on object B, object B simultaneously exerts a force on A that is equal in magnitude, same line of action, but opposite in direction.

Why is it true?

These two forces always act on two different objects, so they never cancel each other — this is the source of rocket thrust, walking, and every interaction between two bodies.

Topics that use this theorem

Related theorems

Step-by-step proofs

No step-by-step proof yet for this theorem.