The density of a substance is defined as mass of the substance per unit volume.
That is:
SI unit of density is ‘kilograms per cubic metre’.
If the density of a substance is more than the density of water, then the substance will be heavier then water and hence sink in water.
If the density of a substance is less than the density of water, then the substance will be lighter than water and hence float in water.
Concept of density
Every substance has different density which is the amount of mass in unit volume of matter.
Perform the following steps:
Step 1: Pour one-quarter cup of honey,
Step 2: Pour one-quarter cup of coloured water gently on top of honey.
Step 3: Pour one-quarter cup of coconut oil on top of the coloured water.
The different liquids are present in different layers.
This is because different substances have different density.
In other words, for the same volume different substances weigh differently.
Heavier substances tend to settle at the bottom, like honey and lighter substances like oil tend to float at the top.
Relative Density/ Specific gravity:
Density of liquid water at room temperature and pressure is 1gram per 1 cubic cm.
This value is treated as a standard and density of any other material (usually liquids) is calculated relative to the density of water, this is called relative densityor specific gravity.
Hence, specific gravity is the ratio of the mass of a substance to that of a reference substance. The density of honey is approx.
, so its specific gravity would be 1.42/1 = 1.42.
Specific gravity is a ratio; therefore it does not have a unit.
It is a dimensionless physical quantity.
If the specific gravity of a substance is below 1 then it will float and if it is greater than 1 it will sink.
The specific gravity of a substance enables us to know if it will float or sink and gives idea about relative mass or relative density.
Archimedes principle states that if a body is submerged partially or fully inside a fluid, the body will experience a force that will be equal to the weight of the fluid displaced.
This principle is used in designing of ships, in lactometers to determine the quality of milk and to determine purity of gold and other metals.
