| Kelvin's statement of second law of thermodynamics: | It is impossible that, at the end of a cycle of changes, heat has been extracted from a reservoir and an equal amount of work has been produced without producing some other effect. |
| Kinetic energy: | The energy possessed by a body due to its motion, it is equal to ½ mv2, where m is the mass and v is the speed of the body |
| Kepler's first law of planetary motion: | Each planet moves in an elliptical orbit, with the sun located at one of the foci. |
| Kepler's second law of planetary motion: | The radius vector joining the planet to the sun covers equal areas in equal intervals of time. |
| Kepler's third law of planetary motion: | The square of the period of a planet is directly proportional to the cube of the radius of the semi major axis of the orbit. |
| Kilocalorie: | The amount of energy required to raise the temperature of one kilogram of water by 1 , 1 Kcal = 1000 calories. |
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