Chapter 10: The Physical Properties of Matter

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This chapter is an overview of things to come. It is intended to demonstrate some things that we would like to understand in subsequent lectures on matter. It raises questions, but is not intended to answer the questions immediately. Aristotle taught us that when beginning a new science (in this case the study of matter), but before one has any understanding, one should things: what is a thing, what is it not, what are the degrees of dissimilarity? But, naming a thing or even knowing its name is not understanding; it is a preliminary kind of knowing. Matter can be classified according to physical state: solid, liquid, gas, and plasma. A "plasma" is a (usually "gaslike") in which positive and negative charged particles are separated and free to move indeplendently. The overwhelming majority of matter in the universe is in the state, including the interiors of stars and much of the matter in the space between the stars. Examples of plasma: matter in a very hot flame, matter inside fluorescent lights, matter along the path of a lightning stroke. Depending on temperature, most matter can exist in each of the four physical states. Nitrogen can be frozen into solid form, but will melt to liquid form as the temperature increases. Eventually, with increasing temperature, liquid nitrogen will evaporate to form a gas, but if heated to a very hot temperature (say 100000 degrees Celsius), it becomes a . The properties of nitrogen change dramatically as it changes physical state. Matter can be classified according to density. Density is defined as per unit and characterizes the matter of which an object is made. Most objects expand when heated so that density (increases, decreases? with increasing temperature. is an important exception near its freezing point. Matter can be classified according to color. The sun and most incandescent lights have a (continuous, discrete?) spectrum of color, i.e., the colors blend together smoothly. If gases are excited by being bumped by a stream of not-too-energetic electrons flowing through them, the gases exhibit a (continuous, discrete?) spectrum, i.e., a spectrum of separated, distinct colors. This discrete spectrum is a very profound puzzle which holds the key to developing an understanding of the atom. Matter can be classified according to electrical conductivity. Some substances are nonconductors in the solid form, but conduct when melted or dissolved in water. These are (ionic, nonionic?) substances. Others do not conduct electricity even when dissolved or melted. These are (ionic, nonionic?) nonconductors. Matter can be classified according to its elastic properties. The elastic constant is defined to be the ratio of a exerted on a substance to the deformation produced by the force. The forces may be forces of compression, tension, or shear and the elastic constant is (same, different?) for the same substance depending on which kind of force is applied.

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