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(Phys.) Symbol p; unit kg m{TAG(tag=>sup)}-3{TAG}. The mass of a material per unit volume. Relative density is defined with respect to water, which has an absolute density of 1000 kg m{TAG(tag=>sup)}-3{TAG} at 4°C and 1 atm. For example, 1 m{TAG(tag=>sup)}3{TAG} of lead, with a relative density of 11.35 at room temperature, has a mass of 11 350 kg.
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Where a large number of small items have a parameter which itself varies over a larger range, it is sometimes useful to express the number of items per unit interval of the parameter as a density of items as a function of the parameter. For example, we can define population density (the items are people, the parameter is position on the chosen map), charge density (the items are point charges, the parameter is position in space), probability density (See continuous random variable) and density of states. The common feature of all such definitions is that the interval over which the items are counted must be much larger than the items themselves, but much smaller than the range of the parameter. |
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