Newton's Third Law

Mechanics · 1687

Equation: F_AB = −F_BA
Field: Mechanics
Named After: Isaac Newton
Symbols: F_AB the force body A exerts on body B · F_BA the force B exerts back on A: equal in size, opposite in direction
Year: 1687

Significance

Forces come in pairs, and the pair acts on two different bodies — which is why they never cancel. A rocket goes up because it pushes exhaust down; a jet engine and a swimmer work the same way. It is the reason momentum is conserved: the two forces in a pair change the two momenta by equal and opposite amounts.

Machines

Gas Turbine (Jet Engine)Solid-Propellant Rocket Motor Liquid-Propellant Rocket Engine

Required By

Conservation of Momentum

Referenced by

equation

Conservation of Momentum

machine

Gas Turbine (Jet Engine)Liquid-Propellant Rocket Engine Solid-Propellant Rocket Motor

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From the Equations database in Notion, last edited 2026-08-18. This page is the row, rendered by the build; nothing on it is written by hand.