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KINEMATIC VISCOSITY - absolute viscosity of a fluid divided by its density at the same temperature of measurement. It is the measure of a fluid’s resistance to flow under gravity, as determined by test method ASTM D 445. To determine kinetic viscosity, a fixed volume of the test fluid is allowed to flow through a calibrated capillary tube (viscometer) that is held at a closely controlled temperature. The kinematic viscosity, in centistokes (cSt), is the product of the measured flow time in seconds and the calibration constant of the viscometer. See viscosity.

KNOCK - in the cylinder of a spark-ignited internal combustion engine, premature explosion of a portion of the air-fuel mixture, independent of spark plug ignition, as a result of excessive heat buildup during compression. The high local pressures resulting from the explosion are the source of the objectionable clatter or ping association with knock. Knock reduces efficiency and can be destructive to engine parts. High-octane gasolines resist knocking. Also called detonation. See octane number, pre-ignition.