poles of a magnet. The locations on a magnet where the lines of magnetic flux leave and where they enter. In a ferromagnetic metal, groups of atoms whose electrons have their spin axes in alignment are called magnetic domains. When all of the domains are aligned in the same direction, the material is magnetized.
All magnets, regardless of their size, have two poles, a north pole and a south pole. Lines of magnetic flux leave the magnet at its north pole and return through its south pole. All the lines of flux leave and enter the poles at right angles to the surface.
polonium. A naturally radioactive, metallic chemical element produced by bombarding bismuth or lead with neutrons. Polonium’s symbol is Po, its atomic number is 84, and the mass number of its most stable isotope is 209.
polyconic projection (map projection). A projection used for laying out the grid of latitude and longitude for a chart or map. In a polyconic projection, the parallels of latitude are represented by arcs of a circle whose center is the north or south pole. The meridians of longitude are straight lines radiating from the poles.
polyester fibers. A synthetic fiber made by the polymerization process, in which tiny molecules are united to form a long chain of molecules. Polyester fibers are woven into fabrics that are known by their trade names of Dacron, Fortrel, and Kodel. Polyester film and sheet are known as Mylar and Celenar.
Cloth woven of polyester fibers for use as an aircraft covering material is sold under such trade names as Poly Fiber, Eonnex, and Ceconite. This cloth is shrunk on the structure with heat, rather than with shrinking dope.
polyester resin (reinforced plastic component). A thermosetting resin serving as the matrix for much of the fiberglass cloth and mat used to make parts for aircraft composite construction.
polyethylene plastic material. A lightweight, chemical-resistant, thermoplastic material. Polyethylene resins are used for making sheets of protective covering material and containers for liquids.
polymerization. A chemical reaction in which several small molecules join together to form larger molecules. The larger molecules are made up of repeating structural units of the original molecules. Polymerization often causes liquid materials to change into a jelly.
polymer paint. A water-based paint that contains vinyl or acrylic resins. When the water evaporates, it leaves a waterproof film of the plastic resin.