What is Density?

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Density is one of the fundamental principles of physics. Density is the reason why a plank of wood floats on water while a piece of metal several times smaller will sink. It is also the reason why water flows much faster than mercury. There are many other areas where density is applicable and evidenced. Now that we know where to look for it, let us see how we can identify and describe it.

Density is a component of mass and volume, it is the mass per unit volume. This means that when you have two objects of similar volume and different weights, the difference is due to one having higher density than the other. A lay definition of density would be that it is how compact substance is packed together. This then translates to mean that when you take a sample of matter it will have its highest density as a solid and the least as a gas. This is because in the solid state, its particles will be more tightly held together than in any other state. Just like in ordinary speech, when someone refers to a dense forest it will mean one where the trees and foliage are very tightly packed with minimal space between them. This is the same with density, higher density means particles and packed more tightly.

Density is measured in kilograms per cubic meter. This unit of measurement may however be adjusted to accommodate smaller or larger measurements. It is calculated by dividing mass by the volume of the object and is represented using a Greek letter rho whose symbol is ρ.

Temperature and pressure are the two factors that influence the density of any substance. A significant change in either temperature or pressure will translate in a change of density which in turn leads to change of state. When water is in frozen and is in solid state, an increase in temperature will reduce its density and lead to change of state into water. A continued rise in its temperature will further reduce its density and lead to gaseous state. Density and state of substance are therefore interlinked and relate as shown above. It is also important to note that for solid and liquid substances, the effect of pressure on their densities is very minimal. It would require a massive change in pressure to cause the density of either to change. However the temperature of gases will easily change with a change in pressure.

There are many areas where the knowledge and understanding of density are applied in everyday life. One of the best examples is having wood float on water. Most people know this as a fact but may not be aware of the reason for this. It is simply the fact that wood has lower density as compared to water. This may confuse some due to the fact that wood is a solid while water is a liquid but it is very important to remember that the relation between state and density can only be applied when working with the same substance.


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