what is density in physics

Density, mass of a unit volume of a material substance. The formula for density is d = M/V, where d is density, M is mass, and V is volume. Density is commonly expressed in units of grams per cubic centimetre. For example, the density of water is 1 gram per cubic centimetre, and Earth’s density is 5.51 grams per cubic centimetre. Density can also be expressed as kilograms per cubic metre (in MKS or SI units). For example, the density of air is 1.2 kilograms per cubic metre. The densities of common solids, liquids, and gases are listed in textbooks and handbooks. Density offers a convenient means of obtaining the mass of a body from its volume or vice versa; the mass is equal to the volume multiplied by the density (M = Vd), while the volume is equal to the mass divided by the density (V = M/d). The weight of a body, which is usually of more practical interest than its mass, can be obtained by multiplying the mass by the acceleration of gravity. Tables that list the weight per unit volume of substances are also available; this quantity has various titles, such as weight density, specific weight, or unit weight. See also specific gravity. The expression particle density refers to the number of particles per unit volume, not to the density of a single particle, and it is usually expressed as n.

Discussion

Confusion of mass and density. Objects have mass. Materials have density.

Density is the ratio of mass to volume for a material.

ρ = m

Units

1000 kg/m3 = 1000 g/l = 1 g/cm3

Density of selected materials (~20 °C, 1 atm)

Density of selected materials (~20 °C, 1 atm)
material	density (kg/m³)	material	density (kg/m³)
acetone	790	kerosene	810
acid, acetic (CH₃COOH)	1,050	lard	919
acid, hydrochloric (HCl)	????	lead	11,350
acid, sulfuric (H₂SO₄)	1,390	lithium	534
air, 100 K	3.556	lithium 6 deuteride	820
air, 200 K	1.746	lungs	400
air, 293 K	1.207	mayonnaise, traditional	910
air, 300 K	1.161	mayonnaise, light	1,000
air, 500 K	0.696	methane, gas, +25 °C	0.656
air, 1,000 K	0.340	methane, liquid, −90 °C	162
alcohol, ethyl (grain)	789.2	milk, cow, heavy cream	994
alcohol, isopropyl (rubbing)	785.4	milk, cow, light cream	1,012
alcohol, methyl (wood)	791.3	milk, cow, whole	1,030
ammonia	771	milk, cow, skim	1,033
aluminum	2,700	mercury	13,594
argon, gas, ~300 K	1.449	monosodium glutamate	1,620
argon, liquid, 87 K	1,430	nickel	8,900
beer, pilsner, 4 °C	1,008	nitrogen (N₂), gas, ~300 K	1.145
benzene	870	nitrogen (N₂), liquid, 74 K	808
blood	1,035	oil, vegetable, coconut	924
body fat	918	oil, vegetable, corn	922
bone	1,900	oil, vegetable, olive	918
butane	551	oil, vegetable, palm	915
butter	911	oil, vegetable, peanut	914
carbon	2,250	oil, vegetable, soya	927
carbon, diamond	3,539	osmium	22,500
carbon dioxide, gas, +25 °C	1.799	oxygen (O₂), gas, ~300 K	1.308
carbon dioxide, solid, −78 °C	1,562	oxygen (O₂), liquid, 87 K	1,155
copper	8,960	perchlorethylene	1,600
corn starch, loosely packed	540	platinum	21,450
corn starch, tightly packed	630	plutonium, α	19,860
corn syrup	1,380	salt (sodium chloride)	2,165
diesel	800	silicon	2,330
formaldehyde	1,130	silicon dioxide (quartz)	2,600
freon 12, liquid	1,311	silicone	993
freon 12, vapor	36.83	silver	10,490
gasoline	803	skin	1,050
glycerine	1,260	sodium bicarbonate	2,200
gold	19,300	sugar, sucrose	1,550
grain, barley	620	titanium	4,500
grain, corn, shelled	720	tungsten	19,300
grain, corn, ear	900	tungsten carbide (WC)	15,630
grain, flax	770	uranium	19,050
grain, millet	640	water, liquid, 100 °C	958.40
grain, oats	410	water, liquid, 50 °C	988.03
grain, rice, rough	580	water, liquid, 30 °C	995.65
grain, rice, hulled	750	water, liquid, 20 °C	998.21
grain, rye	720	water, liquid, 10 °C	999.70
grain, wheat	770	water, liquid, 4 °C	999.98
helium, gas, ~300 K	0.164	water, liquid, 0 °C	999.84
helium, liquid, 4 K	147	water, ice, 0 °C	916
hydrogen (H₂), gas, 300 K	0.082	water, ice, -50 °C	922
hydrogen (H₂), liquid, 17 K	71	water, ice, −100 °C	927
honey	1,420	water, sea	1,025
iron	7,870	water, saline (0.9 % NaCl)	1,004
iridium	22,400	zinc	7,140

Average density of some celestial bodies
object	density (kg/m³)	object	density (kg/m³)
earth, average	5,500	main sequence stars	5~5,000
earth, core	12,500	giant to supergiant stars	10⁻⁴~10⁻⁶
terrestrial planets	3,900~5,200	white dwarf star	10⁵~10⁹
jovian planets	600~1,600	neutron star	10¹⁷~10¹⁸
pluto	1,900	stellar mass black hole	~10¹⁸
comets	~600	supermassive black hole	~10⁷
sun, average	1,400	observable universe	~10⁻²⁶
sun, core	153,000