DENSITY IS THE RATIO OF MASS TO VOLUME

The rate at which a liquid evaporates increases with temperature. A puddle of water, for example, evaporates from a hot pavement more quickly than it does from your cool kitchen floor. When the temperature is hot enough, evaporation occurs beneath the surface of the liquid. As a result, bubbles form and are buoyed up to the surface. We say that the liquid is boiling. A substance is often characterized by its boiling point, which is the temperature at which it boils. At sea level, the boiling point of fresh water is 100°C. 

The transformation from gas to liquid—the reverse of evaporation—is called condensation. This process can occur when the temperature of a gas decreases. The water vapor held in the warm daylight air, for example, may condense to form a wet dew in the cool of the night. 

Density is the amount of mass contained in a sample divided by the volume of the sample  

An object having a mass of 1 gram and a volume of 1 milliliter, for example, has a density of 

Which occupies a greater volume 1 kilogram of lead or 1 kilogram of aluminum  

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Density Is the Ratio of Mass to Volume know as H20. Water molecules are so small that an 8-oz glass of water contains about a trillion trillion of them. 

Volume and density have derived units. Density is the ratio of mass to volume. Density can be used to identify a sample of matter. 

Density is the ratio of mass to volume and is a useful way of characterizing a substance. Values of density are often related to a standard reference, the density of pure water at 4°C. This "referenced" density is the specific gravity, the ratio of the density of the object in question to the density of pure water at 4°C. 

Tamped Density and Tamped Volume (ISO 787, Part II). The tamped density is the ratio of mass to volume, while the tamped volume is the ratio of volume to mass after tamping under specified conditions. These quantities provide information about the volume requirements of the products. 

A piece of cork is lighter than a piece of lead of the same size. Liquid mercury, as shown in Figure 2.7, is heavier than water. In other words, different substances contain different masses per volume. This property is called density. Density is the ratio of mass to volume, or mass divided by volume. Density is expressed by the equation... 

Density is the ratio of mass to volume. Oil floats on water, for example, because, in addition to not mixing with water, oil has a lower density than water. That is, given equal volumes of the two liquids, the oil will have a smaller mass than the water. Density is calculated using the following equation ... 

The density of a material is the ratio of mass to volume. In the metric system it is expressed in grams per cubic centimeter (g/cm or g cm—for liquids and solids and in grams per liter (g/i) for gases. The solubility of a substance in a particular solvent is the amount of substance (the solute) that will dissolve in a given amount (usually 100 g) of the solvent. 

Note that even though mass and volume are extensive properties, the ratio of mass to volume is intensive. Samples of copper weighing 1.00 g, 10.5 g, 264 g,... all have the same density, 8.94 g/mL at 25°C. 

The density of a substance is independent of the size of the sample because doubling the volume also doubles the mass so the ratio of mass to volume remains the same. Density is therefore an intensive property. We distinguish different substances by their intensive properties. Thus, we might recognize a sample as water by noting its color, density (1.00 g-cm-3), melting point (0°C), boiling point (100°C), and the fact that it is a liquid. 

Particle Density Methods Density is defined as the ratio of mass to volume, so the density determination can be separated into two steps measurement of mass and measurement of volume. Determining the mass of an object is rather straightforward however, it is much more difficult to directly determine the volume of a solid. The volume of a solid object with a regular geometric shape may be calculated... 

Another extremely important micromeritic parameter is powder density, which is defined as the ratio of mass to volume. Three types of density, which differ in their determination of volume occupied by the powder, are normally differentiated. Bulk density is obtained by measuring the volume of a known mass of powder sample (that has been passed through a mesh screen) into a suitable volume-measuring apparatus. When a graduated cylinder is used for the measurement, the volume is determined to the nearest milliliter. The bulk... 

Measuring the density of a 100 percent dense ceramic is relatively straightforward. If the sample is uniform in shape, then the volume is calculated from the dimensions, and the weight is accurately measured by using a sensitive balance. The ratio of mass to volume is the density. 

Two other common measures of bone density in biomechanical studies are termed tissue and apparent densities. Tissue density p i is defined as the ratio of mass to volume of the actual bone tissue. It is similar for cortical and trabecular bone, varies little in adult humans, and is about 2.0 g/cm. Apparent density p pp is defined as the ratio of the mass of bone tissue to the bulk volume of... 

Some variables are dependent on the amount of substance present these are called extensive properties. On the other hand, intensive properties are independent of the amount of substance. Mass and volume, for example, are extensive properties, bnt density is an intensive property. Thus, a gallon of water has four times the mass of a quart of water, but it also has four times the volume, so the density, the ratio of mass to volume, is the same for both samples. 

Density is a characteristic physical property of a substance. It does not depend on the size of a sample because as the mass of a sample increases, its volume increases proportionately. The ratio of mass to volume is constant. Therefore, density is one property that can help to identify a substance. Figure 2.8 shows the densities of some common materials. As you can see, cork has a density of only 0.24 g/cm, which is less than the density of liquid water. Because cork is less dense than water, it floats on water. Lead, on the other hand, has a density of 11.35 g/cm. The density of lead is greater than that of water, so lead sinks in water. 

When we compress a sample of gas, we decrease its volume. Because its mass remains the same, the ratio of mass to volume (density) increases. Conversely, if we increase the volume to which a sample of gas is confined, we decrease its density. 

For a fuel ceU stack, mass- and volume-specific power densities are more useful parameters. The mass power density is the ratio of power to stack weight, measured in kilowatts per kilogram. Clearly, light-weight stack materials are required to increase the mass power density of a stack. Volume power density is the ratio of power to stack volume, measured in kilowatts per liter or kilowatts per cubic meter. Thus, for increasing the volume power density, one requires to reduce the stack size and simplify the stack system. 

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