9p1 Density & Relative density


Density and Relative density are quantities used by scientist to examine substances and their differences.

1: DENSITY Is a ratio of Volume and Mass of a particular substance.

Therefore we say; Mass in variation to Volume                              M : V

For any material a ratio is constant for any varying traces.

The Constant density symbolized by Greek letter

There fore;

Example:- Musa had a piece of wire of Aluminum .The mass measured was 81g. He decided to find density after articulate dimensions

SolutionLength of wire = 5cmCross-sectional area = 6cm2Mass = 81g

but   V = A x L …………….(ii)

V = 6cm2 x 5cmV = 30 cm3


= 81g/30cm3   =   2.7 g/cm3A

density of Aluminum = 2.7g/ cm3

The SI unit of Density that negotiated by scientist is g/cm3 or kg/m3.

Due to this a mixture, alloys and pure substance may found their densities .Any substance of definite or undefinite shape may found their densities.

Example:–A mixture of sand and impurities, water and Alcohol e.t.c-An alloys of Brass and solder e.t.c-A pure substance like water, Paraffin,copper ,iron ,Aluminum e.t.c


Aim:-To determine densities of sand and water. Sand:-How to measure Mass of sand and Volume of sand? The Mass of sand and Volume of sand can be found by using empty bottle.


(1)   Pour water into the bottle at the top; and spill into the measuring cylinder. Then record the Volume   of water.

The volume of water is equal to volume of empty space of the battle = Vo           Therefore the sand that will fill this bottle occupy the same volume of that water.

(2)   Measure of empty bottle on the beam balance and record it as Mb

(3)   Fill sand in the bottle and measure the total mass on the beam balance then record it as MT     Therefore; Mass of the sand is calculated as Ms = MT – Mb

In so doing Density of the sand can be calculated as ;


How to measure Mass of water and Volume of water?


(1)   Measure a mass of empty bottle on the beam balance and record it as Mb

(2)   Pour water into the bottle and fill at the top. Then measure a total mass of water and bottle on the beam balance; and records as MT

(3)   Spill water into the measuring cylinder and records volume Vo.

(4)   Calculate density as;Mw = Mass of water as ;Mw = MT – MbVw = Vo


Is not a quantity.

Is just a common number that used to make comparison of different material Since it has been discovered that water has a specific unit density of 1g/cm3 or 1000kg/m3; hence therefore density of water used to make comparison to density of water used to make comparison to densities of other materials.

As the great of relative density is the heavier material than a small relative density.e.g Aluminum R. density=2.7 and Iron R. density=7 This means that Iron is heavier than Aluminum in comparison of the equal shape size. This lead Engineers to prefer Aluminum sheets to manufacture car bodies than Iron sheets. Therefore

relative density;

Is a common number given by a ratio of density of a substance per density of water.


A table of different common materials and their respective Relative densities.

Q :-A liquid and water mixed together and gave a volume of 80cm3 with density of 5g/cm3.

If volume of water is two third of that liquid; find relative density of liquid.


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