2.2 Materials Materials Breithaupt pages 162 to 171

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.

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

Question Calculate the weight of a gold ingot of dimensions (20 x 10 x 4) cm volume of gold = 800 cm3 [ 20x10 - 2 x 10x10 - 2 x 4x10 - 2 ] = 800 x10 - 6 m3 mass = volume x density = 800 x10 - 6 x 19 300 = 15.4 kg weight = 15.4 x 9.81 N weight of gold ingot = 152 N

11. 1 Density

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 150 000 850 to 1400 1017 2 700 > 4 x 1017

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

If r = 2 cm calculate the mass of gold. 11. 1 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 = 3.18 kg Volume of cylinder = π r2 h Calculate the density of aluminium.

Hint: first work out the masses of each metal present 11. 1 Density Density ρ = mass (kg) volume ( m3 ) Hint: first work out the masses of each metal present

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 .

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