Physics 114 – Lecture 36

1. Physics 114 – Lecture 36 • Chapter 13Temperature and Kinetic Theory • §13.1 Atomic Theory of Matter • Democritus speculated about progressive divisions of matter. Would a stage be reached when the matter could not be divided further without changing the nature of that matter? He thought that this would occur. • He defined the smallest individual piece of matter to be an atom of that substance • Mass of an atom – define mass of 12C atom to be 12.0000 unified atomic mass units • → 1 u ≡ 1.6605 X 10-27 kg L36-s1,9

2. Physics 114 – Lecture 36 • Evidence for atomic theory of matter, Brown, 1827, observed random motion of very small particles (pollen grain) suspended in liquid – known as Brownian motion • Einstein, 1905, showed from a theoretical analysis that a typical atomic diameter ~ 10-10 m Brownian Motion Solid Liquid Gas L36-s2,9

3. Physics 114 – Lecture 36 • Study Example 13.1 – Distance between atoms • §13.2 Temperature and Thermometers • Temperature is a measure of how hot or how cold a substance may be • Most substances expand when heated – e.g., expansion joints or compressible spacers are needed to accommodate this effect, bridges, concrete surfaces, … • This expansion may be used to design a thermometer. Other attributes of a substance which changes with temperature may also be used L36-s3,9

4. Physics 114 – Lecture 36 • Examples • Temperature Scales • Need two easily reproducible temperatures • Freezing of water – 00 C ≡ 320 F • Boiling point of water – 1000 C ≡ 2120 F • → Δ T (boiling point of water – freezing point of water) = 1000 C = 1800 F - Celsius and Fahrenheit Temp Scales L36-s4,9

5. Physics 114 – Lecture 36 • Conversion of Fahrenheit temperatures to Celsius temperatures and vice versa • Study Example 13.2 • For very accurate temperature measurement one must use a constant volume gas thermometer – see text L36-s5,9

6. Physics 114 – Lecture 36 • §13.3 Thermal Equilibrium and the Zeroth Law of Thermodynamics • If two bodies at different temperatures are placed in thermal contact they reach a common temperature and are said to be in thermal equilibrium • If bodies A and B are separately in thermal equilibrium with a third body, C, then bodies A and B will be in thermal equilibrium with each other • This statement is known as the zeroth law of therodynamics L36-s6,9

7. Physics 114 – Lecture 36 • §13.4 Thermal Expansion • Linear Expansion • ΔL = α L0ΔT • where α = coefficient of linear expansion • With L = L0 + ΔL → L = L0 (1 + αΔT) • Units of α are (0C)-1 • For most materials α may only be considered constant over a limited range in temperature • Study Examples 13.3, 13.4 and 13.5 L36-s7,9

8. Physics 114 – Lecture 36 • Volume Expansion • ΔV = βV0ΔT • where β = coefficient of linear expansion • With V = V0 + ΔV → V = V0 (1 + βΔT) • Again, units of β are (0C)-1 • If the material is isotropic then it is easily shown that • β ≈ 3α • Notice that the coefficient of linear expansion has no meaning for fluids – liquids and gases – since they have no definite shape L36-s8,9

9. Physics 114 – Lecture 36 • Anomalous Behaviour of Water Below 40C • With the density of water is given by, ρ = m/V • For a given mass of water, at temperature, T, • ρ = m/V = m/[V0(1 + βΔT)] = m/V0X [1/(1 + βΔT)] = ρ0X [1/(1 + βΔT)] L36-s9,9