Internal energy and temperature describe the microscopic behaviour of matter in thermal physics. Internal energy is the total energy stored within a substance, arising from the kinetic energy of its particles (their motion) and the potential energy linked to the forces between them. Temperature, on the other hand, measures the average kinetic energy of those particles and therefore indicates how hot or cold a system is. In this topic you examine how heating changes internal energy, how temperature relates to particle motion, and why different substances require different amounts of energy to raise their temperature or change state. These ideas form the basis for understanding specific heat capacity, latent heat, and the links between microscopic particle models and macroscopic thermal behaviour.

Specific heat capacity measures how much energy is needed to raise the temperature of 1 kg of a substance by 1 °C (or 1 K). It tells you how resistant a material is to heating and how much energy it can store thermally. In this topic you use the relationship, Q=mcΔT to calculate energy changes during heating, and you compare substances to see why some heat up quickly while others change temperature more slowly. You also look at practical methods for determining specific heat capacity experimentally, considering energy losses and how they affect results. Understanding this concept is important for explaining thermal stability, analysing heating processes, and interpreting the thermal behaviour of solids, liquids, and gases.

Gas laws describe how gases behave by linking pressure, volume, temperature, and amount of gas. In this topic you study Boyle’s law, Charles’s law, and the pressure–temperature relationship, each showing how two variables change while the third is held constant. You also combine these ideas into the ideal gas equation, pV=nRT, which provides a practical way to calculate the behaviour of gases under a wide range of conditions. These relationships reflect the motion and collisions of particles in a gas, helping you connect microscopic behaviour to macroscopic measurements. Gas laws form the foundation for understanding engines, atmospheric processes, and many thermal systems.