Density

Density of a substance is defined  as its mass per unit volume.

,           

The unit of density is   

Table of Density of Some Substances

Relative Density or Specific Density

Water is the most common substance and its density is used to compare the density of other material.

Relative density is defined as the ration of density of the substance to density of water

But

Therefore

Also ,

Weight=Mass  x g

Relative density has no units because is a ratio of two substances

Example

If the density of mercury is  , what is its relative density ?

Determination Of Density And Relative Density

For a regular object, for example a cube, the volume can easily be found by measuring its dimension. The mass can be obtained by direct weighing . then the density can be calculated as

For an irregular shaped object, the mass can be obtained by direct weighing . The volume can be obtained by immersing the body in water, provided is not soluble( relative density bottle is used for soluble solids and powder). The volume of water displaced is equal to the volume of the object.

A relative density bottle can be used to find the density of a liquid.

The bottle is weighed empty and also weigh when filled with liquid. Also, the weight is recorded when filled with water.

Example,

A relative density bottle weighs 20g when empty. It weighs 60g when filled with a liquid and 70g when filled with water. What is the relative density and density of the liquid ?

solution

   ,    

,   

This method can be used to obtain the density of powder, sand or soluble solids. Fill the bottle with the  powder and then with the water, measure  the different masses.

Read about Upthrust in Archimedes’ Principle

Read more about PHYSICS for High Schools