mechanical engineering

Density
Density is defined as an objects mass per unit volume. Mass is a property.

• Mass and Weight - the Difference! - What is weight and what is mass? An explanation of the difference between weight and mass.

The density can be expressed as
ρ = m / V = 1 / vg (1)
where
ρ = density (kg/m3)
m = mass (kg)
V = volume (m3)
vg = specific volume (m3/kg)

The SI units for density are kg/m3. The imperial (BG) units are lb/ft3 (slugs/ft3). While people often use pounds per cubic foot as a measure of density in the U.S., pounds are really a measure of force, not mass. Slugs are the correct measure of mass. You can multiply slugs by 32.2 for a rough value in pounds.

• Unit converter for other units

The higher the density, the tighter the particles are packed inside the substance. Density is a physical
property constant at a given temperature and density can help to identify a substance.

• Densities and material properties for common materials

Relative Density
Relative density of a substance is the ratio of the substance to the density of water, i.e.

Example - Use the Density to Identify the Material:
An unknown liquid substance has a mass of 18.5 g and occupies a volume of 23.4 ml. (milliliter).

The density can be calculated as
ρ = [18.5 (g) / 1000 (g/kg)] / [23.4 (ml) / 1000 (ml/l) 1000 (l/m3) ]
= 18.5 10-3 (kg) / 23.4 10-6 (m3)
= 790 kg/m3

If we look up densities of some common substances, we can find that ethyl alcohol, or ethanol, has a density of 790 kg/m3. Our unknown liquid may likely be ethyl alcohol!

Example - Use Density to Calculate the Mass of a Volume
The density of titanium is 4507 kg/m3 . Calculate the mass of 0.17 m3 titanium!
m = 0.17 (m3) 4507 (kg/m3)
= 766.2 kg

Specific Weight
Specific Weight is defined as weight per unit volume. Weight is a force.
* Mass and Weight - the difference! - What is weight and what is mass? An explanation of the difference between weight and mass.
Specific Weight can be expressed as

γ = ρ g (2)
where
γ = specific weight (N/m3)
ρ = density (kg/m3)
g = acceleration of gravity (m/s2)

The SI-units of specific weight are N/m3. The imperial units are lb/ft3. The local acceleration g is under normal conditions 9.807 m/s2 in SI-units and 32.174 ft/s2 in imperial units.

Example - Specific Weight Water
Specific weight for water at 39 oF (4 oC) is 62.4 lb/ft3 (9.81 kN/m3) in imperial units. Specific weight in SI units can be calculates like
γ = 1000 kg/m3 9.81 m/s2
= 9810 N/m3
= 9.81 kN/m3

Type and composition	Condition	Tensile MN/m2	Product	Use
Pure copper 99.95%Cu	O	220	Sheet, strip wire	High conductivity electrical applications
	H	350
98.85%cu	O	220	All wrought forms	Chemical plant. Deep drawn, spun articles
	H	360
99.25%cu +0.5%As	O	220	All wrought forms	Retains strength at high temperatures. Heat exchangers, steam pipes
	H	360
Brasses 9O%Cu, 10%Zn-gilding metal	O	280	Sheet, strip and wire	Imitation jewellery, decorative work
	H	510
7o%cU, 30%Zn-Cartridge brass	O	325	Sheet, strip	High ductility for deep drawing
	H	700
65%Cu, 35%Zn- standard brass	O	340	Sheet, strip and extrusions	General cold working alloy
	H	700
60%Cu, 40%Zn- Muntz metal	M	375	Hot rolled plate and extrusions	Condenser and heat exchanger plates
59%Cu, 35%Zn, 2%Mn, 2%A1, 2%Fe	M	600	Cast and hot worked forms	Ships screws, rudders
58%Cu, 39%Zn, 3%Pb free cutting	M	440	Extrusions	High speed machine parts
Bronzes 95.5%Cu, 3%Sn, 1.5Zn	O	325	Strip	Coinage
	H	725
5.5%Sn, O.l%Zn, Cu	O	360	Sheet, strip and wire	Springs, steam turbine blades
	H	700
10%Sn, 0.03-0.25P, Cu- phosphor bronze	M	280	Castings	Bushes, bearings and springs
10%Sn, O.S%P, Cu	M	280	Castings	General-purpose castings and bearings
10%Sn, 2%Zn, Cu-Admiralty gunmetal	M	300	Castings	Pressure-tight castings, pump,valve bodies
Aluminium bronze 95?'ocU, 5%AI	O	400	Strip and tubing	Imitation jewellery, condenser tubes
	H	770
10Y0A1, 2.5%Fe, 2-5%Ni, Cu	M	700	Hot worked and cast products	High-strength castings and forgings
Cupronickel 75%cu, 25%Ni	O	360	Strip	British 'silver' coinage
	H	600
70%Cu, 30%Ni	O	375	Sheet and tubing	Condenser tubes, good corrosion resistance
	H	650
29%cu, 68%Ni, 1.25%Fe,1.25%Mn	O	550	All forms	Chemical plant, good corrosion resistance
	H	725
Nickel-silver 55%Cu, 27%Zn, l8%Ni	O	375	Sheet and strip	Decorative use and cutlery
	H	650
Ber y llium-copper 1.75-2.5%Be, 0.5% co, c u	WP	1300	Sheet, strip, wire, forgings	Non-spark tools, springs

0 =annealed, M =as manufactured, H =fully work hardened, WP=solution heat treated and precipitation hardened.