The density of a material is defined as its mass per unit volume. The symbol of density is ρ (the Greek letter rho)
Mathematically: ρ = m / V
Where: ρ is the density, m is the mass and V is the volume.
History : In a well-known common story, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a wreath dedicated to the gods and replacing it with another, cheaper alloy.
Mathematically: ρ = m / V
Where: ρ is the density, m is the mass and V is the volume.
History : In a well-known common story, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a wreath dedicated to the gods and replacing it with another, cheaper alloy.
Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the weight; but the king did not approve of this.
Baffled, Archimedes took a relaxing bath and observed from the rise of the warm water upon entering that he could calculate the volume of the gold crown through the displacement of the water. Allegedly, upon this discovery, he went running naked though the streets shouting, "Eureka! Eureka!" (Greek "I found it"). As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment.
In general density can be changed by changing either the "pressure or the temperature". Increasing the pressure will always increase the density of a material.
Baffled, Archimedes took a relaxing bath and observed from the rise of the warm water upon entering that he could calculate the volume of the gold crown through the displacement of the water. Allegedly, upon this discovery, he went running naked though the streets shouting, "Eureka! Eureka!" (Greek "I found it"). As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment.
In general density can be changed by changing either the "pressure or the temperature". Increasing the pressure will always increase the density of a material.
Increasing the temperature generally decreases the density, but there are notable exceptions to this generalisation.
For example, the density of water increases between its melting point at 0 °C and 4 °C and similar behaviour is observed in silicon at low temperatures.
The effect of pressure and temperature on the densities of liquids and solids is small so that a typical compressibility for a liquid or solid is 10–6 bar–1 (1 bar=0.1 MPa) and a typical thermal expansivity is 10–5 K–1.
In contrast, the density of gases is strongly affected by pressure. Boyle's law says that the density of an ideal gas is given by
ρ = MP / RT
Where R is the universal gas constant, P is the pressure, M the molar mass, and T the absolute temperature.
This means that a gas at 300 K and 1 bar will have its density doubled by increasing the pressure to 2 bar or by reducing the temperature to 150 K.
Osmium is the densest known substance at standard conditions for temperature and pressure.
Density of Composite material:
ASTM specification D792 describes the steps to measure the density of a composite material.
ρ = (Wa / (Wa + Ww - Wb )) 0.9975
Where:
ρ is the density of the composite material, in g/cm3 and
Wa is the weight of the specimen when hung in the air
Ww is the weight of the partly immersed wire holding the specimen
Wb is the weight of the specimen when immersed fully in distilled water, along with the partly immersed wire holding the specimen
0.9975 is the density in g/cm3 of the distilled water at 23°C.
For example, the density of water increases between its melting point at 0 °C and 4 °C and similar behaviour is observed in silicon at low temperatures.
The effect of pressure and temperature on the densities of liquids and solids is small so that a typical compressibility for a liquid or solid is 10–6 bar–1 (1 bar=0.1 MPa) and a typical thermal expansivity is 10–5 K–1.
In contrast, the density of gases is strongly affected by pressure. Boyle's law says that the density of an ideal gas is given by
ρ = MP / RT
Where R is the universal gas constant, P is the pressure, M the molar mass, and T the absolute temperature.
This means that a gas at 300 K and 1 bar will have its density doubled by increasing the pressure to 2 bar or by reducing the temperature to 150 K.
Osmium is the densest known substance at standard conditions for temperature and pressure.
Density of Composite material:
ASTM specification D792 describes the steps to measure the density of a composite material.
ρ = (Wa / (Wa + Ww - Wb )) 0.9975
Where:
ρ is the density of the composite material, in g/cm3 and
Wa is the weight of the specimen when hung in the air
Ww is the weight of the partly immersed wire holding the specimen
Wb is the weight of the specimen when immersed fully in distilled water, along with the partly immersed wire holding the specimen
0.9975 is the density in g/cm3 of the distilled water at 23°C.
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