Amount of substance Amount of substance Amount of substance is a standard-defined quantity that measures the size of an ensemble of particles, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount. The International System of Units (SI) defines the amount of substance to be proportional to the number of entities present. The SI unit for amount of substance is the mole. It has the unit symbol mol. The proportionality constant is the inverse of the Avogadro constant. The mole is defined as the amount of substance that contains an equal number of elementary entities as there
Stoic physics Stoic physics Stoic physics is the natural philosophy adopted by the Stoic philosophers of ancient Greece and Rome used to explain the natural processes at work in the universe. To the Stoics, the universe is a single pantheistic God, but one which is also a material substance. The primitive substance of the universe is a divine essence ("pneuma") which is the basis of everything which exists. This "pneuma", which is the active part or reason ("logos") of God, provides form and motion to matter, and is the origin of the elements, life, and human rationality. From their physics, the Stoics