Why are drag car standards constantly reinforced? Drag racing is a highly competitive (and expensive) sport. There are a variety of classes of vehicles, ranging from stock classes (dependent on car weight, engine size, and degree of engine modification) all the way up to the Top Fuel class. Cars in the Top Fuel class may weigh over two thousand pounds, and are capable of top speeds of well over 300 miles per hour at the end of the quarter-mile. The standards for each class are well-defined, and frequent checks are made of engine dimensions and components to ensure that the rules are followed. Physical Properties A physical property is a characteristic of a substance that can be observed or measured without changing the identity of the substance. Silver is a shiny metal that conducts electricity very well. It can be molded into thin sheets—a property called malleability. Salt is dull, brittle, and conducts electricity when it has been dissolved into water (which it does quite easily). Physical properties of matter include color, hardness, malleability, solubility, electrical conductivity, density, melting point , and boiling point . For the elements, color does not vary much from one element to the next. The vast majority of elements are colorless, silver, or gray. Some elements do have distinctive colors: sulfur and chlorine are yellow, copper is (of course) copper-colored, and elemental bromine is red. Density can be a very useful parameter for identifying an element. Of the materials that exist as solids at room temperature, iodine has a very low density compared to zinc, chromium, and tin. Gold has a very high density, as does platinum. Hardness helps determine how an element (especially a metal) might be used. Many elements are fairly soft (silver and gold, for example) while others (such as titanium, tungsten, and chromium) are much harder. Carbon is an interesting example of hardness. In graphite (the "lead" found in pencils) the carbon is very soft, while the carbon in a diamond is roughly seven times as hard. Melting point and boiling point are somewhat unique identifiers, especially in the case of compounds. In addition to giving some idea as to the identity of the compound, important information can be obtained about the purity of the material. Is that Really Gold? Archimedes and Density How do you determine the density of an irregularly shaped object? Learn how Archimedes did this thousands of years ago with just a beaker, water, and some simple math. Summary A physical property is a characteristic of a substance that can be observed or measured without changing the identity of the substance. Physical properties include color, density, hardness, melting point, and boiling point. Review What is a physical property? What color are most metals? Is titanium harder or softer than gold?