Definition
A relationship between two quantities in which one increases as the other decreases, in proportion. If one quantity doubles, the other is halved; if one is reduced to a third, the other is tripled. Their product remains constant.
Plain English
When two things are in inverse ratio, one goes up as the other goes down, by the same proportion. Bigger one side, smaller the other.
Context Anchor
Seen in aviation ground school when describing relationships such as air pressure and air volume, or other situations where one value changes opposite to another.
Derivation
From Latin inversus, meaning 'turned upside down,' and ratio, meaning 'a reckoning' or 'relationship between numbers.' So inverse ratio literally means a 'turned-around relationship' — one quantity goes up while the other goes down.
Why Pilots Care
Understanding inverse relationships helps predict how changes in one flight variable affect another, such as power output versus altitude in normally aspirated engines.
Analogy
Think of a seesaw: when one side goes up, the other goes down by the same amount. An inverse ratio works the same way — the two values move in opposite directions in proportion.
Grounding Statement
If a sealed amount of air is squeezed into half the space, its pressure rises because the volume went down.
Intuition Check
Inverse ratio does not mean the two things are unrelated. It means they are related in opposite directions: one increases while the other decreases in a matching way.
Example Sentence 1
Pressure and volume of a gas at constant temperature vary in inverse ratio: squeeze the gas into half the space and the pressure doubles.
Example Sentence 2
The relationship between propeller RPM and available torque often follows an inverse ratio at constant manifold pressure.