Mathematics and Physics Glossary

Pachometer n. (Phys.) An instrument for measuring thickness, as of the glass of a mirror, or of paper; a pachymeter.

Packing fraction, n. (Phys.) The quotient of the algebraic difference between the isotopic mass and the mass number of a nuclide, divided by its mass number, often interpreted as a measure of stability.

Pair, n. (Mech.) In a mechanism, two elements, or bodies, which are so applied to each other as to mutually constrain relative motion.

Pancratic a. (Opt.) Having all or many degrees of power; having a great range of power; said of an eyepiece made adjustable so as to give a varying magnifying power.

Pandigital, n. (Math.) a number or expression is one which contains each of the digits 0 to 9 once and once only.

Parabola n.; pl. Parabolas. (Geom.) (a) A kind of curve; one of the conic sections formed by the intersection of the surface of a cone with a plane parallel to one of its sides. It is a curve, any point of which is equally distant from a fixed point, called the focus, and a fixed straight line, called the directrix. See Focus. (b) One of a group of curves defined by the equation y = axⁿ where n is a positive whole number or a positive fraction. For the cubical parabola n = 3; for the semicubical parabola n = ³/₂. See Cubical parabola, and Semicubical parabola. The parabolas have infinite branches, but no rectilineal asymptotes.