1. 2.2 Materials Materials
Breithaupt pages 162 to 171

2. AQA AS Specification Lessons Topics 1 to 4 Bulk properties of solids
Density
ρ = m / V
Hooke’s law, elastic limit, experimental investigations.
F = k ΔL
Tensile strain and tensile stress.
Elastic strain energy, breaking stress.
Derivation of energy stored = ½ FΔL
Description of plastic behaviour, fracture and brittleness; interpretation of simple stress-strain curves.
5 & 6
The Young modulus
The Young modulus = tensile stress = FL
tensile strain AΔL
One simple method of measurement.
Use of stress-strain graphs to find the Young modulus.

3. The density of a substance is defined as its mass per unit volume.
Density ρ ( rho) = mass (kg)
volume ( m3 )
The unit for density is the kilogram per cubic metre kg / m3
Note: 1 g cm-3 is the same as 1000 kg m-3

4. Question
Calculate the weight of a gold ingot of dimensions (20 x 10 x 4) cm
volume of gold = 800 cm [ 20x x 10x x 4x ]
= 800 x m3
mass = volume x density
= 800 x x = 15.4 kg
weight = x 9.81 N
weight of gold ingot = 152 N

5. Density

6. Density examples iron hydrogen lead helium mercury air uranium gold
/ kg m-3
Interstellar medium
iron
hydrogen
lead
helium
mercury
air
uranium
wood (average)
gold
lithium
water
Sun’s core
plastics
neutron star
aluminium
black hole
10-25 to 10-15
7 900
0.0989
11 300
0.179
13 500
1.29
19 100
19 300
700
osmium
0.534
22 610
1000
850 to 1400
1017
2 700
> 4 x 1017

7. Answers Complete: density mass volume 240 g 40 cm3 3000 kg m-3 4500 kg

8. If r = 2 cm calculate the mass of gold.
Density
Density ρ = mass (kg)
volume ( m3 )
r = 0.05m
h = 0.15m
Density of Gold = 19.3 kg / m3
Volume of sphere = 4/3 π r3
If r = 2 cm calculate the mass of gold.
Mass of Aluminium = kg
Volume of cylinder = π r2 h
Calculate the density of aluminium.

9. Hint: first work out the masses of each metal present
Density
Density ρ = mass (kg)
volume ( m3 )
Hint: first work out the masses of each metal present

11. Internet Links
Balloons & Bouyancy - PhET - Experiment with a helium balloon, a hot air balloon, or a rigid sphere filled with different gases. Discover what makes some balloons float and others sink.
Density Lab - Explore Science
Floating Log - Explore Science .

12. Notes on Density from Breithaupt pages 162 & 163
Define what is meant by density, include the equation.
Calculate (a) the volume of copper that has a mass of 178 kg; (b) the mass of 14.4m3 of air; (c) the density of a solid of mass 2000kg and volume 3m3.
State the density of (a) a metallic solid; (b) water & (c) air
(a) Explain why a density of 1000 kgm-3 is the same as one of 1 g cm-3. (b) What is the density of water in g mm-3?
Explain how to measure the density of (a) a regular solid; (b) a liquid and (c) an irregular solid.
Try the Summary Questions on page 163