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| In some cases density is expressed as the dimensionless quantities specific gravity (SG) or [[relative]] density (RD), in which case it is expressed in multiples of the density of some other standard material, usually water or air/gas. | | In some cases density is expressed as the dimensionless quantities specific gravity (SG) or [[relative]] density (RD), in which case it is expressed in multiples of the density of some other standard material, usually water or air/gas. |
− | ===[edit]History=== | + | ===History=== |
| In a well-known story, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a wreath dedicated to the gods and replacing it with another, cheaper alloy.[1] Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the weight; but the king did not approve of this. | | In a well-known story, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a wreath dedicated to the gods and replacing it with another, cheaper alloy.[1] Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the weight; but the king did not approve of this. |
| Baffled, Archimedes took a relaxing immersion bath and observed from the rise of the warm water upon entering that he could calculate the volume of the gold crown through the displacement of the water. | | Baffled, Archimedes took a relaxing immersion bath and observed from the rise of the warm water upon entering that he could calculate the volume of the gold crown through the displacement of the water. |
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| This story first appeared in written form in [[Vitruvius]]' [[books]] of [[architecture]], two centuries after it supposedly took place.[2] Some scholars have doubted the accuracy of this tale, saying among other things that the [[method]] would have required precise measurements that would have been difficult to make at the time. [3][4] | | This story first appeared in written form in [[Vitruvius]]' [[books]] of [[architecture]], two centuries after it supposedly took place.[2] Some scholars have doubted the accuracy of this tale, saying among other things that the [[method]] would have required precise measurements that would have been difficult to make at the time. [3][4] |
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| ===Measurement of density=== | | ===Measurement of density=== |
| For a homogeneous object, the [[mass]] divided by the volume gives the density. The mass is normally measured with an appropriate scale or balance; the volume may be measured directly (from the [[geometry]] of the object) or by the displacement of a fluid. Hydrostatic weighing is a [[method]] that combines these two. | | For a homogeneous object, the [[mass]] divided by the volume gives the density. The mass is normally measured with an appropriate scale or balance; the volume may be measured directly (from the [[geometry]] of the object) or by the displacement of a fluid. Hydrostatic weighing is a [[method]] that combines these two. |