Changes

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.  

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]

===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.