Heat The "molar heat capacity" is the heat capacity per unit amount (SI unit: mole) of a pure substance, and the "specific heat capacity", often called simply "specific heat", is the heat capacity per unit mass of a material. Heat capacity is a physical property of a substance, which means that it depends on the state and properties of the substance under consideration. The specific heats of monatomic gases, such as helium, are nearly constant with temperature. Diatomic gases such as hydrogen display some temperature dependence, and triatomic gases (e.g., carbon dioxide) still more. Before the development of the laws of
Cross section (physics) of the colliding system are , and , before and after the collision respectively, the differential cross section is given by where the on-shell matrix is defined by in terms of the S-matrix. Here is the Dirac delta function. The computation of the S-matrix is the main goal of the scattering theory. Although the SI unit of total cross sections is m, smaller units are usually used in practice. In nuclear and particle physics, the conventional unit is the barn b, where 1 b = 10 m = 100 fm. Smaller prefixed units such as mb and μb are also