The Physics of Heat
We all have an intuitive understanding of heat and fire, which has long been important to human households for warmth and cooking. With the combustion of wood in small fires people were able to move energy from tree branches and direct it into cooking pots and the immediate space around the hearth. Our Stone Age ancestors knew perfectly well that by touching dry wood with a flame, raising its temperature, it could be combusted, and that once the wood had finished burning then only ash would remain. It must have been obvious even then that the wood was used up, its energy taken out as heat. Since that time, human ingenuity has developed technology and a whole civilization based around heat, power and the internal combustion engine.