Definition
Three foundational laws of classical mechanics formulated by Sir Isaac Newton that describe the relationship between forces acting on a body and the motion of that body. (1) The Law of Inertia: a body at rest remains at rest, and a body in motion continues in motion at a constant speed and in a straight line, unless acted upon by an outside force. (2) The Law of Acceleration: the acceleration of a body is directly proportional to the net force applied to it and inversely proportional to its mass (F = ma). (3) The Law of Action and Reaction: for every action there is an equal and opposite reaction. Together these laws govern how aircraft accelerate, decelerate, turn, climb, and descend, and they underpin the production of lift, thrust, drag, and weight.
Plain English
Three rules that explain how things move. First, things keep doing what they're doing unless something pushes or pulls them. Second, the harder you push something, the faster it speeds up — and heavier things need a bigger push. Third, every push produces an equal push back the other way.
Context Anchor
Seen in basic aerodynamics when explaining lift, weight, thrust, drag, turns, climbs, descents, and why the aircraft responds the way it does to control inputs.
Derivation
Named after Sir Isaac Newton, the English physicist who published these laws in 1687 in his work Philosophiae Naturalis Principia Mathematica. Knowing the laws come from classical physics — not from anything aviation-specific — is helpful because it shows that flying an aircraft obeys the same rules as any other moving object.
Why Pilots Care
Understanding these laws explains why an airplane behaves the way it does when power, attitude, or configuration changes.
Grounding Statement
Picture the airplane in flight: it will not change its path unless the air, engine, gravity, or pilot-controlled surfaces create a push or pull that changes it.
Intuition Check
Newton's Three Laws of Motion are not aviation regulations or checklist rules. They are physical laws that describe how objects, including aircraft, move when forces act on them.
Example Sentence 1
By Newton's Third Law, the propeller pushes air rearward and the air pushes the aircraft forward with an equal and opposite force.
Example Sentence 2
When the pilot advances the throttle, the resulting increase in thrust follows the second law to produce acceleration.