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(Encyclopedia)porcupine, member of either of two rodent families, characterized by having some of its hairs modified as bristles, spines, or quills. The quills are loosely attached to the porcupines' skin and pull ...

pitch, in aviation

(Encyclopedia)pitch, in aviation: see airplane; airfoil. ...

pitch, in music

(Encyclopedia)pitch, in music, the position of a tone in the musical scale, today designated by a letter name and determined by the frequency of vibration of the source of the tone. Pitch is an attribute of every m...

Pleiades, in astronomy

(Encyclopedia)Pleiades plēˈədēz, plīˈ– [key], in astronomy, famous open star cluster in the constellation Taurus; cataloged as M45. The cluster consists of some 500 stars, has a diameter of 35 light-years, ...

plum, in botany

(Encyclopedia)plum, common name for a tree of any of many species of the genus Prunus of the family Rosaceae (rose family) and for its fruit, a drupe. The plum is generally cultivated in the temperate zones, though...

Pluto, in astronomy

(Encyclopedia)Pluto, in astronomy, a dwarf planet and the first Kuiper belt, or transneptunian, object (see comet) to be discovered (1930) by astronomers. Pluto has an elliptical orbit usually lying beyond that of ...

power, in mathematics

(Encyclopedia)power, in mathematics: see exponent. ...

power, in physics

(Encyclopedia)power, in physics, time rate of doing work or of producing or expending energy. The unit of power based on the English units of measurement is the horsepower, devised for describing mechanical power b...

precipitation, in chemistry

(Encyclopedia)precipitation, in chemistry, a process in which a solid is separated from a suspension, sol, or solution. In a suspension such as sand in water the solid spontaneously precipitates (settles out) on st...