K

Source edition 1965. Please read the Introduction to find out about this dictionary and our plans for it. Caution, many entries have not been updated since the 1965 edition.
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Karman street = Karman vortex street.

Karman vortex street

(After Theodore von Karman, 1881-1963, Hungarian-born American scientist). A double trail of vortices formed alternately on both sides of a cylinder or similar body moving at right angles to its axis through a fluid, the cortices in one row rotating in a direction opposite to that of the other row.

K-band

A frequency band used in radar extending approximately from 10.9 gigacycles per second to 36 gigacycles per second.

K-corona

That portion of the radiation from the solar corona consisting of the continuous spectrum scattered by electrons.

K-display

In radar, a modified A-display in which a target appears as a pair of vertical deflections or blips instead of a single deflection. When the radar antenna is correctly pointed at the target in azimuth, the blips are of equal height. When not correctly pointed, the difference in blip height is an indication of direction and magnitude of azimuth pointing error. Also called K-scan, K-scope, K-indicator.

Kelvin scale = Kelvin temperature scale.

Kelvin temperature scale (abbr K)

An absolute temperature scale independent of the thermometric properties of the working substance. On this scale, the difference between two temperatures T1 and T2 is proportional to the heat converted into mechanical work by a Carnot engine operating between the isotherms and adiabats through T1 and T2. Also called absolute temperature scale, thermodynamic temperature scale.

For convenience the Kelvin is identified with the Celsius degree. The ice point in the Kelvin scale is 273.15 degrees K. The triple point of water, the fundamental reference points, is 273.16 degrees K. See absolute zero, approximate absolute temperature scale, Rankine temperature scale.

Kennelly-Heaviside layer = E-layer.

Kepler equation

In celestial mechanics M = E - e sin E where M is mean anomaly; E is eccentric anomaly; and e is eccentricity of the orbital ellipse. See anomaly, note.

Keplerian

Pertaining to motion in conformance with Kepler laws, as Keplerian trajectory, Keplerian ellipse.

Kepler laws

The three empirical laws governing the motions of planets in their orbits, discovered by Johannes Kepler (1571-1630). These are: (a) the orbits of the planets are ellipses, with the sun at a common focus; (b) as a planet moves in its orbit, the line joining the planet and sun sweeps over equal areas in equal intervals of time (also called law of equal areas ); (c) the squares of the periods of revolution of any two planets are proportional to the cubes of their mean distances from the sun.

Kepler planetary laws = Kepler laws.

kilo (abbr k)

Prefix meaning multiplied by 1000.

kilocalorie (abbr kcal)

See calorie.

kilocycle (abbr kc)

One thousand cycles or 1000 cycles per second.

kilogram (abbr kg)

The unit of mass in the metric system; the mass of the International Prototype Kilogram, a cylinder of platinum-iridium alloy, stored at Seures, France, by the International Bureau of Weights and Measures.

kilogram calorie (abbr kg-cal, Kcal, Cal)

See calorie.

kilomegacycle = gigacycle.

kilometer (abbr km)

A unit of distance in the metric system.

1 kilometer = 3280.8 feet = 1093.6 yards = 1000 meters = 0.62137 statute miles = 0.53996 nautical miles.

kilometric waves

See frequency bands.

K-indicator = K-display.

K-indices = magnetic K-indices.

kinematic eddy viscosity

See kinematic viscosity.

kinematics

The branch of mechanics dealing with the description of the motion of bodies or fluids without reference to the forces producing the motion.

kinematic viscosity (symbol v)

A coefficient defined as the ratio of the dynamic viscosity of a fluid to its density.

The kinematic viscosity of most gases increases with increasing temperature and decreasing pressure. For dry air at 0 degrees C, the kinematic viscosity is about 0.13 square centimeter per second. In the theory of atmospheric turbulence the kinematic viscosity is usually replaced by the kinematic eddy viscosity to account for the increased internal friction due to turbulence.

kinetic energy (symbol E_k)

The energy which a body possesses as a consequence of its motion, defined as one-half the product of its mass m and the square of its speed v, 1/2 mv². The kinetic energy per unit volume of a fluid parcel is the 1/2 p v2 , where p is the density and v the speed of the parcel. See potential energy.

For relativistic speeds the kinetic energy is given by E_k = mc² - m₀c² where c is the velocity of light in a vacuum, m₀ is the rest mass, and m is the moving mass.

kinetic-energy equation = mechanical-energy equation.

kinetic pressure = dynamic pressure.

kinetic theory

The derivation of the bulk properties of fluids from the properties of their constituent molecules, their motions, and interactions.

kink instability

In plasma physics, a kinking or bending of a current-carrying filament in the pinch effect geometry.

If a slight bend forms in the plasma column of a pinch, the magnetic forces are such as to increase the bend and the column is unstable.

Kirchhoff law

The radiation law which states that at a given temperature the ratio of the emissivity to the absorptivity for a given wavelength is the same for all bodies and is equal to the emissivity of an ideal black body at that temperature and wavelength.

Loosely put, this important law asserts that good absorbers of a given wavelength are also good emitters of that wavelength. It is essential to note that the Kirchhoff law relates absorption and emission at the same wavelength and at the same temperature. Also called Kirchhoff radiation law.

klystron

An electron tube for converting direct-current energy into radio frequency energy by alternately speeding up and slowing down the electrons. See magnetron.

knot

A nautical mile per hour, 1.1508 statute miles per hour.

Knudsen flow

The flow of gases through ducts and tubes under conditions intermediate between laminar viscous flow and molecular flow. Also called transition flow.

Knudsen gage

A gage which measures pressure in terms of the net rate of transfer of momentum by molecules between two surface maintained at different temperatures and separated by a distance smaller than the mean free path of the gas molecules. Also called radiometer vacuum gage.

Various types of Knudsen gage are distinguished by the names of the inventors and differ mainly in the shape and method of suspension of the movable element.

Knudsen number

A number used to describe the flow of a low density gas, equal to the ratio λ/l where λ is the mean free path of the gas molecule and l is a characteristic length, such as boundary layer thickness, or apparatus dimension.

The Knudsen number is used most commonly to define the extend to which the gas behaves like a collection of independent particles (free-molecule regime, Knudsen number much larger than unity), or like a viscous fluid (continuous regime, Knudsen number much smaller than unity). Intermediate regimes are termed transition region, and slip flow region. See rarefied gas dynamics, note.

Knudsen rate of evaporation = maximum evaporation rate.

K-scan = K-display.

K-scope = K-display.