Definition
A principle of classical mechanics stating that the acceleration of a body is directly proportional to the net force acting on it and inversely proportional to its mass, expressed as Force = Mass × Acceleration (F = ma). In its momentum form, it states that the net force on a body equals the rate of change of its momentum (where momentum is mass times velocity).
Plain English
If you push on something, how fast it speeds up depends on how hard you push and how heavy it is. A bigger push makes it accelerate faster. A heavier object needs a bigger push to get the same acceleration.
Context Anchor
Seen in aerodynamics discussions that explain how thrust, drag, lift, weight, and control inputs change an aircraft’s motion.
Derivation
Named after Sir Isaac Newton, who published these laws of motion in 1687. 'Momentum' comes from the Latin 'movimentum,' meaning movement or motion — fitting, since momentum measures how much motion an object has.
Why Pilots Care
Understanding this law lets pilots anticipate how power changes, turns, or wind affect airspeed and path, improving control and safety in instrument conditions.
Analogy
Pushing an empty cart is easy; pushing a loaded cart takes more force to get the same change in speed. An aircraft works the same way: more mass takes more force to change its motion.
Grounding Statement
Push harder, and an aircraft accelerates faster. Load it heavier, and the same push produces less acceleration.
Intuition Check
Momentum does not mean motivation or “keeping going” in a casual sense here. It means the motion an object has because it has mass and speed, and a force is needed to change that motion.
Example Sentence 1
Newton's Second Law explains why the same engine produces less acceleration on takeoff when the aircraft is loaded to maximum gross weight.
Example Sentence 2
In a level turn the pilot must add power to maintain airspeed since part of lift is now used to change direction.