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Exploring Design, Technology, & Engineering © 2012 Chapter 5: Materials and Technology—Terms and Definitions acoustical property: a quality of a material governing how it reacts to sound waves. Materials absorbing the waves are said to be insulators, while those carrying sound are called transmitters. alloy: a mixture of two or more elements. ceramic: inorganic (never living) matter made up of crystals. Types include clay-based, refractories, and glass. chemical processing: using chemicals to change the form of materials. The chemicals change the structure of the material’s molecules. chemical property: a quality controlling how a material will react to chemicals. For example, some materials will corrode or form rust. Others will resist corrosion. composite: a solid material combining two or more materials, yet each material retains its own properties. Concrete is an example. It combines cement, sand, and gravel, but none of the ingredients change. ductility: the ability of a material to be pulled, stretched, or hammered without breaking. electrical property: the quality controlling a material’s reaction to electrical current. engineering material: solid matter which has a set, rigid structure. Solids maintain this structure without support from a container. Metals, ceramics, polymers, and composites are the four major types of engineering materials. exhaustible resource: a material that, once used, can never be replaced. Examples are fossil fuels, such as coal and petroleum. hazardous material: any substance that exposes people to a health risk. hazardous waste: an unwanted by-product of technology that exposes people to a health risk. magnetic property: the quality describing a material’s reaction to magnetic forces. mechanical processing: changing material by cutting, crushing, pounding, or grinding into a new form. mechanical property: the quality of a material that affects how it reacts to mechanical force and loads. This property affects how the material will react to twisting, pulling, and squeezing forces. metal: inorganic (never living) material which is usually in a solid form. Other marks of a metal are its opacity, ductility, and conductivity. natural resource: a material that appears in nature. optical property: the quality governing a material’s reaction to light. Some materials absorb light, some reflect light, and others allow the light to pass through. physical property: a basic feature of material, such as density, moisture content, and smoothness. plastic: synthetic (human-made) organic materials designed and produced to meet specific needs. polymer: organic (once living) matter usually made from natural gas or petroleum. Wood can,

Copyright Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. however, also be changed into a polymer. property: a characteristic of a material. There are seven properties: physical, mechanical, chemical, thermal, electrical and magnetic, optical, and acoustical. renewable resource: a material that can be replaced. thermal conductivity: the measurement of heat moving through a material. thermal expansion: a state in which materials are heated and become longer and wider. thermal processing: using heat to change material into a more useful form. thermal property: a material’s reaction to heat. Heat may expand some materials. Certain materials allow heat to travel through them easily. Others resist movement of heat.