The texts contain definitions. An important term is bolded and its definition can usually be found in the same or following sentence. In chemistry and physics, an everyday word has its own, well-defined meaning, which differs from the everyday meaning.  In everyday life, water means, for example , washing, drinking or bathing water. In chemistry, water (H2O) is a substance formed from hydrogen and oxygen. Therefore, general knowledge alone is not enough, but the definitions of chemistry and physics must be learned.