Density

Grade 9 science

What is Density?

• Density is a PHYSICAL property of matter

• It is a Quantitative property as it can be measured

• It is a way of comparing “heaviness” of objects

• It is the heaviness (mass) compared to a specific volume.

If each ball has the same mass which cube will weigh more?

Each box has the same volume

Which is heavier?

• 1Kg of Feathers or 1Kg of Lead?

• Both weigh the same but the feathers will take up a lot more space (volume) than the same amount of lead.

• Why?• The lead is more dense….

Density calculated

• Since density is a comparison of mass to volume these two measurements are needed.

• Density = Mass (grams) Volume (millilitres)

D = M V

Calculating Mass

• The mass of an object can be measured using a Balance.

Calculating Volume

• Can be measured if the object is regular shape.

• Volume of a Cube = length X width X height.• Cylinder = πr2 X height

What about odd shaped objects?

Archimedes figured it out….

Calculating volume by Displacement.

An object placed into an overflow can will displace its own volume of water which can then be measured.

The volume is measured in mL or cc (cubic centimeters)

Problem.

Is Julie’s ring pure gold?

What about this one?

Coke Diet Coke

Volume (mL)

355 355

Mass (g)

394 355

Density D = M V

394 g = 1.11g/mL355 mL

355g = 1.00g/mL355mL

Density of Some Common Substances

Substance Density (g/cm3)  

Air 0.0013                

Feathers 0.0025                

Wood(Oak) 0.6 - 0.9                

Ice  0.92                 

Water  1.00                 Bricks  1.84                

Aluminum  2.70                

Steel  7.80                

Silver  10.50                

Gold  19.30                 

Density of common substances

Material Density

(gm/cm^3)

Liquids

Water at 4 C 1.0000

Water at 20 C 0.998

Gasoline 0.70

Mercury 13.6

Milk 1.03

MaterialDensity(gm/cm^3)

Solids

Magnesium 1.7

Aluminum 2.7

Copper 8.3-9.0

Gold 19.3

Iron 7.8

Lead 11.3

Platinum 21.4

Uranium 18.7

Osmium 22.5

Ice at 0 C 0.92

The G.R.A.S.P. or G.R.A.S.S. method

• Given• Required to find• Analysis• Substitution• Paraphrase (final answer) OR

Solution

Example

• A piece of iron has a volume of 12m3

and a mass of 94,800kg. What is the density of the iron.

G. V= 12m3

M= 94,800kgR.Density of IronS.D = m V

• S. D = 94,800kg 12m3

S. Density = 7,900kg/m3

Convert to g/cm3 1kg = 1000g. 1m3 = 1000cm3 Therefore answer =7.9g/cm3