NEWTON THIRD LAW

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. Whenever Object A exerts a force on Object B, Object B exerts a force of equal magnitude in the opposite direction back on Object A.

\vec{F}_{\text{A on B}} = -\vec{F}_{\text{B on A}}

Core Properties of Force Pairs

• Equal in magnitude: Both forces are identical in strength.
• Opposite in direction: One force acts directly against the vector of the other.
• Act on different objects: Action and reaction forces never cancel each other out because they are exerted on two separate entities (e.g., foot pushes ground backward; ground pushes foot forward).
• Simultaneous: Neither force occurs before or after the other; both exist at the exact same instant.

Real-World Examples

• Walking: Your shoe pushes backward on the pavement (Action); the pavement pushes forward on your shoe (Reaction), propelling you.
• Rocket Propulsion: High-pressure gas is expelled downward out of the engine nozzle (Action); an equal upward thrust force pushes the rocket into the sky (Reaction).
• Recoil of a Firearm: Expanding gas pushes the projectile out of the barrel forward (Action); an equal force pushes the gun rearward against the shooter's shoulder (Reaction).