This module is about how heat is transferred and also ways to reduce the rate at which that happens.
Heat is the movement of particles, in solids, it is just vibration, in liquids, the particles move, but are still touching and in gases, the particles do not touch and move very fast.
Heat flows from hot to cold - from where energy is, to where it isn’t.
Temperature is a value that represents that energy and the movement of particles.
Radiation is “heat travelling like light”; everything radiates a certain amount of infra-red radiation - heat rays. These travel in straight lines at the speed of light. You know this because a shady area on a Summer’s day is cooler than a sunny one. Even people give out some infra-red, that’s how burglar alarms know you are there.