Definition
The natural law stating that every object with mass attracts every other object with mass, with the strength of the attraction increasing as the masses get larger and decreasing as the distance between them increases. On Earth, this law is what produces weight and what makes objects fall toward the ground when unsupported.
Plain English
Everything that has mass pulls on everything else that has mass. The bigger the objects, the stronger the pull. The farther apart they are, the weaker the pull. On Earth, this pull is what we feel as gravity holding us and our aircraft down.
Context Anchor
Encountered in basic aerodynamics when explaining why an aircraft has weight and why lift is needed in flight.
Derivation
From Latin universalis (applying to all) and gravitas (heaviness, weight). The name reflects Newton's insight that the same force pulling an apple to the ground also holds the Moon in orbit -- one rule, applying everywhere, to everything.
Why Pilots Care
It explains the gravitational force felt as weight that lift must overcome for flight and that slightly decreases with altitude.
Grounding Statement
When an airplane is parked, Earth pulls it downward; when the airplane is flying, that same downward pull is still there.
Intuition Check
“Universal” does not mean vague or general here. It means the rule applies to all objects with mass, everywhere.
Example Sentence 1
Universal gravitation is the reason an aircraft must produce lift equal to its weight in order to maintain level flight.
Example Sentence 2
At cruising altitude the aircraft is slightly farther from Earth's center so the pull of universal gravitation is marginally less.