Definition
A unit of kinematic viscosity in the centimeter-gram-second (CGS) system, equal to one square centimeter per second (cm²/s). It expresses how readily a fluid flows under the influence of gravity, accounting for both its resistance to flow and its density.
Plain English
A measurement of how easily a fluid flows. A fluid with a low stoke value flows easily, like water; one with a high stoke value flows slowly, like cold engine oil.
Context Anchor
Seen in discussions of smoke, fire, and ventilation inside the airplane.
Derivation
Named after Sir George Gabriel Stokes, a 19th-century Irish mathematician and physicist whose work on fluid motion led to the equations describing how fluids flow. Knowing the unit is named after a person — not the everyday word 'stoke' meaning to feed a fire — helps avoid confusion.
Why Pilots Care
Engine oils, hydraulic fluids, and fuels are specified by their viscosity. Using a fluid with the wrong viscosity rating can affect engine lubrication, cold-weather starting, and overall system performance.
Grounding Statement
A small flame can grow quickly if it is given a fresh supply of air.
Intuition Check
Do not read stoke as simply “start a fire.” In this context, it means to feed an existing fire and make it burn stronger, often by adding air.
Example Sentence 1
The oil's viscosity, measured in stokes, increases sharply as outside temperatures drop, which is why preheating may be required before a cold-weather start.
Example Sentence 2
During the go-around, he stoked the throttle to full power for the missed approach.