kappa curve: Also known as Gutschoven's curve with equation y²(x² + y²) = a²x². So class="d-title" named (kappa) due to its similarity with the greek letter kappa

kelvin: The SI unit of temperature usually denoted by K. One degree Kelvin is the same as one degree Celsius, although Kelvin starts counting from the coldest temperature possible (the ideal state when there is no associated kinetic energy in the particles).

Kendall's coefficient of concordance: See coefficient of concordance.

Kendall's rank correlation coefficient: See correlation coefficient.

Kepler's conjecture: The optimal way to pack balls of radius one into a three-dimensional space is to centre the balls at the points on a cubic lattice.

Kepler's laws: Kepler's Laws of Planetary Motion, three laws pulished by John Kepler early in the seventeenth century.

(1) Every planet orbits the Sun in an ellipse where the Sun is at one of the 2 foci of the ellipse.

(2) The line that joins the Sun to any orbiting planet sweeps out areas at a constant rate (that is, the rate is the same for all points in the orbit).

(3) The squares of the period of orbit is proportional to the cube of the length of the major axes of the orbit (ellipse).

kilo-: A prefix that denotes "a thousand".

kilogram: The SI unit for mass, usually denoted kg. The unit is based on the mass of a litre of water, and it should be very close to the mass of a litre of water (in certain strict conditions), although that is not the definition.

kinematics: The study of position, displacement, distance, speed, velocity and acceleration without taking other "irrelevant" physical factors into account. (So long as it does not affect the aforementioned measures.)

kinetic energy: Energy possessed by an object due to its motion.

kinetics: The study of forces and motion (of which force is a cause).

kite: A convex quadrilateral (non-equiangular and non-equilateral) that has exactly one line of symmetry that runs through 2 of its vertices. (If it has more than one such line of symmetry then it is a rhombus or a square.)