Density

Density
Common symbols
ρ
D
SI unitkg/m3
A graduated cylinder containing various coloured liquids with different densities

The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho), although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:[1]

where ρ is the density, m is the mass, and V is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume,[2] although this is scientifically inaccurate – this quantity is more specifically called specific weight.

For a pure substance the density has the same numerical value as its mass concentration.Different materials usually have different densities, and density may be relevant to buoyancy, purity and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser.

To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density" or "specific gravity", i.e. the ratio of the density of the material to that of a standard material, usually water. Thus a relative density less than one means that the substance floats in water.

The density of a material varies with temperature and pressure. This variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object and thus increases its density. Increasing the temperature of a substance (with a few exceptions) decreases its density by increasing its volume. In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid. This causes it to rise relative to more dense unheated material.

The reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density; rather it increases its mass.

History

In a well-known but probably apocryphal tale, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a golden wreath dedicated to the gods and replacing it with another, cheaper alloy.[3] Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass; but the king did not approve of this. Baffled, Archimedes is said to have taken an immersion bath and observed from the rise of the water upon entering that he could calculate the volume of the gold wreath through the displacement of the water. Upon this discovery, he leapt from his bath and ran naked through the streets shouting, "Eureka! Eureka!" (Εύρηκα! Greek "I have found it"). As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment.

The story first appeared in written form in Vitruvius' books of architecture, two centuries after it supposedly took place.[4] Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time.[5][6]

From the equation for density (ρ = m/V), mass density has units of mass divided by volume. As there are many units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per cubic metre (kg/m3) and the cgs unit of gram per cubic centimetre (g/cm3) are probably the most commonly used units for density. One g/cm3 is equal to one thousand kg/m3. One cubic centimetre (abbreviation cc) is equal to one millilitre. In industry, other larger or smaller units of mass and or volume are often more practical and US customary units may be used. See below for a list of some of the most common units of density.

Other Languages
Afrikaans: Digtheid
Alemannisch: Dichte
العربية: كثافة
aragonés: Densidat
অসমীয়া: ঘনত্ব
azərbaycanca: Sıxlıq
تۆرکجه: سیخلیق
বাংলা: ঘনত্ব
Bân-lâm-gú: Bi̍t-tō͘
беларуская: Шчыльнасць
беларуская (тарашкевіца)‎: Шчыльнасьць
भोजपुरी: घनत्व
български: Плътност
Boarisch: Dichtn
bosanski: Gustoća
català: Densitat
čeština: Hustota
Cymraeg: Dwysedd
dansk: Massefylde
Deutsch: Dichte
eesti: Tihedus
Ελληνικά: Πυκνότητα
español: Densidad
Esperanto: Denso
فارسی: چگالی
français: Masse volumique
Frysk: Tichtheid
furlan: Densitât
Gaeilge: Dlús
Gàidhlig: Dluthad
galego: Densidade
한국어: 밀도
հայերեն: Խտություն
हिन्दी: घनत्व
hrvatski: Gustoća
Igbo: Density
Bahasa Indonesia: Massa jenis
íslenska: Eðlismassi
italiano: Densità
Basa Jawa: Massa jenis
ಕನ್ನಡ: ಸಾಂದ್ರತೆ
ქართული: სიმკვრივე
қазақша: Тығыздық
Kiswahili: Densiti
Kreyòl ayisyen: Dansite
kurdî: Tîrbûn
Кыргызча: Тыгыздык
latviešu: Blīvums
Lëtzebuergesch: Dicht
lietuvių: Tankis
la .lojban.: denmi
lumbaart: Densità
magyar: Sűrűség
македонски: Густина
മലയാളം: സാന്ദ്രത
मराठी: घनता
მარგალური: პისქვინი
مصرى: الكثافه
Bahasa Melayu: Ketumpatan
монгол: Нягт
မြန်မာဘာသာ: သိပ်သည်းခြင်း
नेपाली: घनत्व
日本語: 密度
Napulitano: Denzetà
Nordfriisk: Sachthaid
norsk: Tetthet
norsk nynorsk: Tettleik
ਪੰਜਾਬੀ: ਸੰਘਣਾਪਣ
Plattdüütsch: Dicht
polski: Gęstość
português: Densidade
română: Densitate
русский: Плотность
Scots: Density
shqip: Dendësia
sicilianu: Dinsitati
සිංහල: ඝනත්වය
Simple English: Density
slovenščina: Gostota
ślůnski: Gynstość
کوردی: چڕی
српски / srpski: Густина
srpskohrvatski / српскохрватски: Gustina
suomi: Tiheys
svenska: Densitet
தமிழ்: அடர்த்தி
తెలుగు: సాంద్రత
Türkçe: Yoğunluk
українська: Густина
اردو: کثافت
Tiếng Việt: Khối lượng riêng
Winaray: Kasuok
吴语: 密度
Yorùbá: Kíkisí
粵語: 密度
中文: 密度