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Density

Have you ever thought that if an object takes some space then what this physical property is. This is named as density which shows the denseness of material in a specific given area. This is taken as mass per unit volume of given object. It’s a unique physical property for a particular object. In a qualitative term, it shows how much heavy an object is at constant volume.

We can take a simple example of a leakage oil tank in the ocean then oil drops starts to float on the water due to their less density the water. This is useful for separation of oil from water. Generally the density of water is taken as standard value for calculating the density of substances. If a substance is less dense then it will float on water while it will sink in case of high dense than water. Let’s discuss how it can be measured by its formula, relative density, and about the instrument for measuring density of the liquid.

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There are various formula for density. They are:
$Density$ = $\frac{mass}{volume}$

Here mass is expressed in kg and volume in cubic meters.
$Density$ = $\frac{weight}{volume}$

Density for an ideal gas can be derived by using the following relation:
We have,
 $PV = nRT$

$Density$ =$\frac{M P}{R T}$
Where,
P is the pressure
T is the temperature
M is the mass
R is the universal gas constant
M is actually the molar mass

The above equation gives the mass density relation.

Densities of solutions are expressed in a different way. It is the addition of the mass concentrations of the components of that solution.
Density $\rho$ = $\sum_{i}\rho_{i}$

Use below widget to calculate the density according to the formula.


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Units

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The SI unit of density is kilograms per cubic meter or can be written as kg/m3. Liters and metric tons are also used as other types of units.

Some other units are:
Kilograms per liter or can be written as kg/L
Grams per milliliter or can be written as g/mL
Metric tons per cubic meter or can be written as t/m3
* Kilograms per cubic decimeter or can be written as kg/dm3
Grams per cubic centimeter or can be written as g/cc, gm/cc or g/cm3
Mega grams per cubic meter or can be written as Mg/m3

In U.S. customary unit’s density can be stated in:
Avoirdupois ounces per cubic inch or can be written as oz/cu in
Slugs per cubic foot
Avoirdupois pounds per cubic inch or can be written as lb/cu in
Pounds per cubic foot or can be written as lb/cu ft
Pounds per cubic yard or can be written as lb/cu yd
Pounds per U.S. liquid gallon or can be written as lb/gal
Pounds per U.S. bushel or can be written as lb/bu
There are certain imperial units that are not used these days.

How to Find Density?

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The process of calculating density is quite simple. It is basically the mass divided by volume.
  1. In simple cases we will be provided with two quantities. They are, mass and volume.
  2. Convert the given mass of the object in kg if not in this unit.
  3. Now convert the volume in cubic meter if not in the given unit.
  4. Simply divide mass by volume to find the density.
  5. The units of the answer are kg/m3.
  6. Similarly other formula for density of solution can be used like $\rho$ = $\sum_{i}\rho_{i}$ for calculating the needed density.
For example: If the mass of the substance is 10 kg and the volume is 100 m3 then the density would be calculated as,
Density = $\frac{Mass}{Volume}$ = $\frac{10}{100}$ = 0.1 kg /m3

Density Measurement

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If we consider a homogenous body then the density would be equal to total mass divided by total volume. The mass can be measured by any weighing instrument. The volume can be measured using the instrument called Hydrometer. The volume can also be measured using the displacement of the fluid. For a non homogenous body, the measurement process is quite different, the density is dependent on the location where it is measured. Hence at a particular location density can be found by calculating the density of the tiny volume around that particular location.

In this case, the density = $\frac{\Delta m}{\Delta v}$

Hydrometer

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Hydrometer is an instrument used for determining the density of a liquid. It usually consists of a glass float with a long thin stem which is graduated. The glass float is a large hollow bulb which increases the buoyancy so that the hydrometer floats. The narrow stem increases the sensitivity of the hydrometer. The bottom of the hydrometer is made heavier by loading it with lead shots so that it floats vertically.

Hydrometer

It works on the principle of floatation. It sinks more in a lighter liquid so as to displace more volume of the lighter liquid whose weight is equal to the weight of the hydrometer. Hence, it will sink less in a denser liquid so that it has to displace less volume of the denser liquid whose weight will be equal to the hydrometer. Thus, the lowest density is marked on the top of the stem of a hydrometer and the maximum density is marked at the bottom of the graduated stem.

Relative Density

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Specific gravity is another term for relative density. It is defined as the ratio of the density of a given substance with respect to the density of a given reference material whose density is already known.If we consider Relative density with respect to water then it is termed as Specific gravity. The term "Relative Density" is often used in modern science as compared to relative density. If for a given substance the calculated relative density comes out to be less than 1 then it is said to be less dense than the given reference material.

If for a given substance the calculated relative density comes out to be more than 1 then it is said to be more dense than the given reference material. If the reference material to be considered is water and specific density is calculated then a substance with a relative density that is less than one will not sink in water, it will float for sure. For example, if an ice cube is considered it will float as the specific density is less then 1.

Some of the prerequisites for calculating the relative density are that the temperature and pressure must be known for both the sample and the reference. Pressure to be used is mostly 1 atm. Temperatures may vary from industry to industry

Application of Specific gravity is in industries for obtaining information about the concentration of solutions of various materials such as brines and acids. It is a dimension less quantity.

The formula for Relative Density is RD = $\frac{P_{substance}}{P_{reference}}$.

It can have various applications.
  • It can be used for the determination of the density of the substance by using another substance density which is known.
  • It can be used to quantify the Buoyancy.
  • It can be used for finding out the minerals present in the rock by geologists and scientists.
  • It can be used in industries for finding the concentrations of the liquids or chemical present.
  • It can be measured using a Hydrometer. It can be determined using a Pycnometer. There are various other instruments for the measurement of relative density.

Air Density

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The density of air is denoted by the Greek letter '$\rho$ called Rho. It is the mass per unit volume of Earth's atmosphere basically. It has its applications in aeronautics and other branches of science. Air density depends upon Altitude, it is inversely proportional to it. It is inversely proportional to Air Pressure. It is dependent on temperature or humidity variances.
  • At sea level and at 15°C air density is approximately 1.225 kg/m3 according to ISA (International Standard Atmosphere).
  • It can be written as 0.0023769 slugs/ft3.

Energy Density

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Energy density is defined as the amount of energy that is stored in a given system or a given region considering the space per unit volume.
• Mostly the extractable energy is quantified because it is the only useful energy.
• This means that chemically inaccessible energy is not taken into consideration such as rest mass.
• Quantifiable or measurable energy is basically the energy that posses quantified magnitude with some related units.

If we take fuels then the density is considered to be a very useful parameter.
  • For example if we consider the effectiveness of hydrogen fuel as compared to gasoline then hydrogen has a higher specific energy than gasoline. If energy storage applications are considered, the energy density basically is the ratio of the total mass of the stored energy and the volume of the storage facility, example, the fuel tank.
  • The higher the energy density of the fuel, the more energy may be stored or transported for the same amount of volume. The energy density per unit mass for a fuel is called the specific energy of that particular fuel.
  • Energy density does not tell anything about energy conversion efficiency or energy that is embodied.

Density of Ice

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Water in frozen or solid state is called ice. It has various forms like flakes etc. The reference material to be considered is water and specific density is calculated then a substance with a relative density that is less than one will not sink in water, it will float for sure. If an ice cube is considered it will float as the specific density is less than 1.

• The ice is 8.3% less dense than liquid water approximately.
• The value of density is 0.9167 $\frac{g}{cm^{3}}$.
• This is at zero degree temperature.
• The density of frozen water decreases as the temperature decreases.
• It is 0.9340 $\frac{g}{cm^{3}}$ at −180 °C.
The transmission of an optical medium measurement for a given wavelength is called optical density. Higher the value of optical density lower would be the transmittance and vice - verse.
For example: The optical density value of 1 conveys that 90% of incident light is absorbed.
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The relative density, when reference material is water, is called specific density. Reference material to be considered is water and specific density is calculated then a substance with a relative density that is less than one will not sink in water, it will float for sure. For example, if an ice cube is considered it will float as the specific density is less than 1. The density of water is known to be approximately equal to 1 gram per cubic meter.
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More topics in Density
Optical Density Density of Water
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