L36-s1,9

Physics 114 – Lecture 36• Chapter 13 Temperature 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-s2,9

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-s3,9

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-s4,9

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-s5,9

Physics 114 – Lecture 36• Conversion of Fahrenheit temperatures

to Celsius temperatures andvice versa

• Study Example 13.2• For very accurate temperature

measurement one must use aconstant volume gasthermometer – see text

32 CT5

9 FT and 32 - FT

9

5 CT 0000

L36-s6,9

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-s7,9

Physics 114 – Lecture 36• §13.4 Thermal Expansion• Linear Expansion

• ΔL = α L0 ΔT

• where α = coefficient of linear expansion

• With L = L0 + ΔL → L = L0 (1 + α ΔT)

• 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-s8,9

Physics 114 – Lecture 36• Volume Expansion

• ΔV = βV0 ΔT

• where β = coefficient of linear expansion

• With V = V0 + ΔV → V = V0 (1 + β ΔT)

• 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-s9,9

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/V0 X [1/(1 + βΔT)] = ρ0 X [1/(1 + βΔT)]