The symbol that is most often used to represent density is ρ. Dome also use the Latin D. The equation is ρ = m/V (density equals mass divided by volume). An object's density is determined by the lass of the molecules and how tight the atoms are packed together. A brick has tightly packed atoms and molecules with a lot of mass, making it high density and heavy. In comparison Styrofoam has loosely packed atoms (and lots of air and holes), and not much mass so it is low density and light. Density determines what will float. Objects that are lighter density than water will float - such as the Styrofoam. Wood is low density. Sponge and cork and peppers will float because they are low density. An object with a density less than 1 gm/cm3 will float in water. High density materials such as metal, concrete, or glass, will sink in water because they are higher density than water. An object with a density greater than 1 gm/cm3 will sink in water. The density of water can be changed by the addition of minerals. Density can be used to identify minerals, which have specific density measurements. The common way to express density is Pounds per cubic foot (US customary units), or grams per milliliter (International System of Units). It is difficult to determine the volume of an irregularly shaped object, which makes it more difficult to determine that object's density. The density of gas is difficult to measure because it can change when the pressure or temperature changes. When measuring density, it is important to know that increased pressure will increase density. When measuring density it is important to know that increasing the temperature will decrease the volume (with exceptions). Water is one exception as it becomes denser as the temperature increases from 0°Celsius to 4°Celsius. Density is important when constructing buildings, airplanes, and ships, because weight and weight distribution are important considerations for safety. The energy density of some materials can be used to create power, such as that found in uranium and thorium. The energy density of uranium is 1,539,842,000 MJ/L, and this material is used for power plants, nuclear reactors, and industrial process heat. The energy density of a lithium battery is 4.32 MJ/L and is used to power a portable flashlight. One pound of feathers is equal to the weight of one pound of gold. But the space needed to make up one pound of feathers is much greater, because the feathers are less dense than the gold.
