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  • Define density.
  • Calculate the mass of a reservoir from its density.
  • Compare and contrast the densities of various substances.

Which weighs more, a ton of feathers or a ton of bricks? This old riddle plays with the distinction between mass and density. A ton is a ton, of course; but bricks have much greater density than feathers, and so we are tempted to think of them as heavier. (See [link] .)

Density , as you will see, is an important characteristic of substances. It is crucial, for example, in determining whether an object sinks or floats in a fluid. Density is the mass per unit volume of a substance or object. In equation form, density is defined as

ρ = m V , size 12{ρ= { {m} over {V} } } {}

where the Greek letter ρ size 12{ρ} {} (rho) is the symbol for density, m size 12{m} {} is the mass, and V size 12{V} {} is the volume occupied by the substance.

Density

Density is mass per unit volume.

ρ = m V , size 12{ρ= { {m} over {V} } } {}

where ρ size 12{ρ} {} is the symbol for density, m size 12{m} {} is the mass, and V size 12{V} {} is the volume occupied by the substance.

In the riddle regarding the feathers and bricks, the masses are the same, but the volume occupied by the feathers is much greater, since their density is much lower. The SI unit of density is kg/m 3 size 12{"kg/m" rSup { size 8{3} } } {} , representative values are given in [link] . The metric system was originally devised so that water would have a density of 1 g/cm 3 size 12{1`"g/cm" rSup { size 8{3} } } {} , equivalent to 10 3 kg/m 3 size 12{"10" rSup { size 8{3} } `"kg/m" rSup { size 8{3} } } {} . Thus the basic mass unit, the kilogram, was first devised to be the mass of 1000 mL of water, which has a volume of 1000 cm 3 .

Densities of various substances
Substance ρ ( 10 3 kg/m 3 or g/mL ) size 12{ρ` \( "10" rSup { size 8{3} } `"kg/m" rSup { size 8{3} } `"or"`"g/mL" \) } {} Substance ρ ( 10 3 kg/m 3 or g/mL ) size 12{ρ` \( "10" rSup { size 8{3} } `"kg/m" rSup { size 8{3} } `"or"`"g/mL" \) } {} Substance ρ ( 10 3 kg/m 3 or g/mL ) size 12{ρ` \( "10" rSup { size 8{3} } `"kg/m" rSup { size 8{3} } `"or"`"g/mL" \) } {}
Solids Liquids Gases
Aluminum 2.7 Water (4ºC) 1.000 Air 1 . 29 × 10 3 size 12{1 "." "29" times "10" rSup { size 8{ - 3} } } {}
Brass 8.44 Blood 1.05 Carbon dioxide 1 . 98 × 10 3 size 12{1 "." "98" times "10" rSup { size 8{ - 3} } } {}
Copper (average) 8.8 Sea water 1.025 Carbon monoxide 1 . 25 × 10 3 size 12{1 "." "25" times "10" rSup { size 8{ - 3} } } {}
Gold 19.32 Mercury 13.6 Hydrogen 0 . 090 × 10 3 size 12{0 "." "090" times "10" rSup { size 8{ - 3} } } {}
Iron or steel 7.8 Ethyl alcohol 0.79 Helium 0 . 18 × 10 3 size 12{0 "." "18" times "10" rSup { size 8{ - 3} } } {}
Lead 11.3 Petrol 0.68 Methane 0 . 72 × 10 3 size 12{0 "." "72" times "10" rSup { size 8{ - 3} } } {}
Polystyrene 0.10 Glycerin 1.26 Nitrogen 1 . 25 × 10 3 size 12{1 "." "25" times "10" rSup { size 8{ - 3} } } {}
Tungsten 19.30 Olive oil 0.92 Nitrous oxide 1 . 98 × 10 3 size 12{1 "." "98" times "10" rSup { size 8{ - 3} } } {}
Uranium 18.70 Oxygen 1 . 43 × 10 3 size 12{1 "." "43" times "10" rSup { size 8{ - 3} } } {}
Concrete 2.30–3.0 Steam 100º C size 12{ left ("100""°C" right )} {} 0 . 60 × 10 3 size 12{0 "." "60" times "10" rSup { size 8{ - 3} } } {}
Cork 0.24
Glass, common (average) 2.6
Granite 2.7
Earth’s crust 3.3
Wood 0.3–0.9
Ice (0°C) 0.917
Bone 1.7–2.0
A pile of feathers measuring a ton and a ton of bricks are placed on either side of a plank that is balanced on a small support.
A ton of feathers and a ton of bricks have the same mass, but the feathers make a much bigger pile because they have a much lower density.

As you can see by examining [link] , the density of an object may help identify its composition. The density of gold, for example, is about 2.5 times the density of iron, which is about 2.5 times the density of aluminum. Density also reveals something about the phase of the matter and its substructure. Notice that the densities of liquids and solids are roughly comparable, consistent with the fact that their atoms are in close contact. The densities of gases are much less than those of liquids and solids, because the atoms in gases are separated by large amounts of empty space.

Take-home experiment sugar and salt

A pile of sugar and a pile of salt look pretty similar, but which weighs more? If the volumes of both piles are the same, any difference in mass is due to their different densities (including the air space between crystals). Which do you think has the greater density? What values did you find? What method did you use to determine these values?

Questions & Answers

are nano particles real
Missy Reply
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
Lohitha
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
How we can toraidal magnetic field
Aditya Reply
How we can create polaidal magnetic field
Aditya
4
Mykayuh Reply
Because I'm writing a report and I would like to be really precise for the references
Gre Reply
where did you find the research and the first image (ECG and Blood pressure synchronized)? Thank you!!
Gre Reply
Practice Key Terms 1

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Source:  OpenStax, Physics 101. OpenStax CNX. Jan 07, 2013 Download for free at http://legacy.cnx.org/content/col11479/1.1
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