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# What is Density?

o The principle of density was discovered by a Greek scientist named Archimedes.

o Density is a physical property that is defined as mass divided by its volume.

o Everything around us has mass, it is a fundamental property and plays a role in two other important properties which are volume and density.

o The SI unit of mass is kilograms or grams and it is a measure of the amount of matter present in an object.

o Volume is defined as a three-dimensional space that an object occupies it is expressed in cubic metre.

o Thus, Density is the ratio of mass to volume and the SI unit of density is expressed as kg per metre cube (kg/m3) or per gram per centimeter cube(g/cm3).

o By definition, density is the measurement of how closely or loosely a matter is packed into a certain volume.

## Everyday Examples of Density

o Wood floats on water because it has less density than that of water.

o Helium balloons rise in the air because helium gas has less density as compared to that of surrounding air.

o Ice floating on water is also an example of density which can be attributed to the Archimedes principle.

o Oil spills- when an oil tanker leaks on ocean/water body the oil floats on the water since oil has less density as compared to that of water and this helps to clean up the oil spills from surface of the earth.

### Factors Affecting Density

o Density differs according to temperature and pressure.

o Temperature: As the temperature rises, most substances enlarge or increase their volume.

o This results in the decrease in density.

o Similarly, when the temperature goes down, the density of the substance increases.

o Thus, density is inversely proportional to temperature.

o Pressure: As pressure rises, density increases.

o Similarly, when pressure decreases density decreases because the inter molecular force of attraction decreases.

o Thus, density is directly proportional pressure.

o To sum up the above statements, density is inversely proportional to temperature and directly proportional to pressure exerted on a substance.

###### Change of Phase

o Liquids are less dense as compared to solids because solids have densely packed particles whereas particles of liquid that can slide around.

o Example; Density of water at its freezing point is 0.999 g/cm3, whereas density of ice is 0.92 g/cm3.

o Gases are less dense as compared to liquids because the particles of are free and can move around.

o When a liquid changes into a gas, its volume rises vividly, thus reducing the density of the substance.

o Example; Water has a density of 1.03 g/cm3 at 100°C, whereas the density

###### Change in Volume

o The volume of a substance changes with change in its temperature and pressure. Thus, in turn, it changes the density of the substance.

#### Density of Water

o The density of pure water is taken as 1 g/cm3.

o The water density depends on the purity of water.

o As pure water is less dense as compared to the saline water.

o When the purity of water molecules decreases, the density of water increases.

o Contamination in the water interrupts the density of water.

o Due to contamination, the density of water rises and this change in density depends on the degree of contamination and the temperature.

o Water is also identified as the universal solvent and it is the key component of fluids found in all organisms.

o Water is profusely available on the Earth and is found in all forms that is gas, liquid and solid.

o When the temperature reduces, water changes into solid and when the temperature rises, water changes into gas.

o At the room temperature, water is present in the liquid state.

##### Why Density is Important?

o Density is significant because it defines whether the given substance will rise or sink.

o So, understanding density has main inferences for the motions of substances and gases in the atmosphere and materials floating or sinking in water (H2O).

o By determining of the densities of substances, help us in their separation techniques.

o For instance, separation of oil from the water.

o Another significant application of density is determining whether a substance will float on or will sink in water.

o Example for the same include the floating of ships and diving of submarines which happens due to their density difference.

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