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molecular weight

(Encyclopedia)molecular weight, weight of a molecule of a substance expressed in atomic mass units (amu). The molecular weight may be calculated from the molecular formula of the substance; it is the sum of the ato...

dentistry

(Encyclopedia)dentistry, treatment and care of the teeth and associated oral structures. Dentistry is mainly concerned with tooth decay, disease of the supporting structures, such as the gums, and faulty positionin...

designer drug

(Encyclopedia)designer drug, chemical substance synthesized in a laboratory that is intended to have effects similar to those of a drug that is a controlled substance, such as methamphetamine, marijuana, LSD, or an...

seafloor spreading

(Encyclopedia)CE5 Schematic model of the oceanic crust, showing seafloor spreading seafloor spreading, theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwate...

Union Pacific Railroad

(Encyclopedia)Union Pacific Railroad, transportation company chartered (1862) by Congress to build part of the nation's first transcontinental railroad line. Under terms of the Pacific Railroads Act, the Union Paci...

pesticide

(Encyclopedia)pesticide, biological, physical, or chemical agent used to kill plants or animals that are harmful to people; in practice, the term pesticide is often applied only to chemical agents. Various pesticid...

X ray

(Encyclopedia)CE5 Typical X-ray composite spectrum (intensity as a function of frequency) X ray, invisible, highly penetrating electromagnetic radiation of much shorter wavelength (higher frequency) than visibl...

lubrication

(Encyclopedia)lubrication, introduction of a substance between the contact surfaces of moving parts to reduce friction and to dissipate heat. A lubricant may be oil, grease, graphite, or any substance—gas, liquid...

gas laws

(Encyclopedia)gas laws, physical laws describing the behavior of a gas under various conditions of pressure, volume, and temperature. Experimental results indicate that all real gases behave in approximately the sa...

compound

(Encyclopedia)compound, in chemistry, a substance composed of atoms of two or more elements in chemical combination, occurring in a fixed, definite proportion and arranged in a fixed, definite structure. A compound...