Newton's Third Law
Action–reaction pairs — equal magnitude, opposite direction, act on different bodies.
Key Notes
To every action there is an equal and opposite reaction.
Action and reaction act on DIFFERENT bodies — they never cancel each other out.
The pair always has: same magnitude, opposite direction, same line of action, same type (both gravitational, both normal, etc.)
Rocket propulsion, walking, and swimming all rely on the third law.
Formulas
Third Law
Force of A on B is equal and opposite to force of B on A.
Important Points
Weight (mg on book) and normal force (N from table) are NOT a third-law pair — they act on the same body. The third-law pair of mg is the pull of the book on Earth.
Newton's Third Law notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 11 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.