Definition
A physical law stating that every mass attracts every other mass with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them. In aviation, it is the reason an aircraft has weight: Earth's mass pulls the aircraft's mass downward toward the center of the Earth.
Plain English
Everything with mass pulls on everything else with mass. The Earth pulls the airplane down, and that pull is what we call weight.
Context Anchor
Seen when studying Newton’s laws and the basic forces acting on an aircraft, especially the downward force of weight.
Derivation
From Latin gravitas, meaning 'heaviness.' 'Universal' means it applies to all matter, everywhere — not just on Earth. Knowing that helps the pilot see weight not as a property of the airplane alone, but as the result of Earth pulling on it.
Why Pilots Care
This law accounts for the downward force of weight that must be opposed by lift for sustained flight.
Grounding Statement
If you hold a wrench out at arm's length and let go, it falls. That same pull acts on every part of the aircraft, every second of flight.
Intuition Check
Do not read “universal” as meaning “about the universe only.” Here it means gravity is a rule that applies to all objects with mass, including an aircraft and Earth.
Example Sentence 1
Because of the law of universal gravitation, the aircraft has weight that the wings must support through lift.
Example Sentence 2
During weight-and-balance calculations the pilot accounts for the gravitational attraction described by the law of universal gravitation.