Thermal Physics

Explore how particles explain states of matter, temperature, changes of state and thermal energy transfer.

Chapter navigation

Study the topics in order so the particle model supports the later ideas about thermal energy transfer.

2.1 Kinetic particle model of matter States of matter, particle motion, changes of state, diffusion, Brownian motion and gas pressure. 2.2 Thermal properties and temperature Thermal expansion, temperature measurement, specific heat capacity, melting, boiling and evaporation. 2.3 Transfer of thermal energy Conduction, convection, infrared radiation and their applications in everyday situations.

Big picture

Chapter Overview

Thermal physics studies matter, temperature, internal energy and the ways thermal energy moves. The chapter begins with the kinetic particle model. In this model, all matter is made of particles whose arrangement, movement and energy explain the observable properties of solids, liquids and gases.

Heating a substance transfers energy to it. This usually increases the kinetic energy of its particles, so its temperature rises. During a change of state, however, energy is used to change particle separation and overcome attractive forces. The temperature remains constant until the change is complete.

Thermal expansion explains why gaps are left in bridges and railway tracks. Specific heat capacity explains why equal masses of different substances require different amounts of energy for the same temperature rise.

Evaporation occurs when energetic particles escape from the surface of a liquid. The particles left behind have a lower average kinetic energy, so the liquid cools.

Thermal energy is transferred through conduction, convection and radiation. Conduction is particularly important in solids, convection occurs in liquids and gases, and infrared radiation can travel through a vacuum. Real situations frequently involve more than one transfer process.

Particle model Microscopic particle behaviour explains visible properties.

Energy and temperature Heating changes internal energy, temperature or state.

Energy transfer Conduction, convection and radiation transfer thermal energy.

How the topics fit together

Concept Connections

1 Start with particles
Learn how particle arrangement and motion differ in solids, liquids and gases.
2 Connect motion to temperature
A higher temperature means a greater average kinetic energy of particles.
3 Follow energy during heating
Energy may raise temperature, produce expansion or cause a change of state.
4 Track energy transfer
Use particle collisions, density changes and infrared radiation to explain transfer.

Chapter reference

Key Equations

Use SI units before substituting values and include a unit with every final answer.

Quantity	Equation	Symbols and units	Course
Specific heat capacity	ΔE = mcΔθ	ΔE in J, m in kg, c in J/(kg °C), Δθ in °C	Core
Constant-temperature gas relationship	p₁V₁ = p₂V₂	p is pressure and V is volume. Use consistent units.	Extended

The gas relationship applies to a fixed mass of gas at constant temperature.

Recommended order

Study Route

First pass

Understand the models

Draw particle diagrams and explain observations using particle arrangement, movement and energy.

Second pass

Master explanations

Use complete cause-and-effect explanations for expansion, evaporation, conduction and convection.

Final pass

Apply and calculate

Practise specific heat capacity and gas calculations, then apply the transfer processes to unfamiliar situations.

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