The adiabatic index of a gas, is the ratio of its specific heat capacity at constant pressure (C_P) to its specific heat capacity at constant volume (C_V). It is denoted by the greek letter γ (gamma) or the greek letter κ (kappa). Gas (actually, as), the GNU assembler, is the default GCC back-end. ... The specific heat capacity (symbol c or s, also called specific heat) of a substance is defined as heat capacity per unit mass. ... Pressure is the application of force to a surface, and the concentration of that force in a given area. ... Volume (also called capacity) is a quantification of how much space an object occupies. ... The Greek language is written in the Greek alphabet, developed in classical times (ca 9th century B.C.) and passed down to the present. ... Gamma (upper case Γ, lower case γ) is the third letter of the Greek alphabet. ... Kappa (upper case Κ, lower case κ) is the tenth letter of the Greek alphabet. ...

γ = C_P / C_V

To understand this definition consider the following experiment:  A closed cylinder with a locked piston is filled with air.  This cylinder is heated.  Since the piston cannot move the volume is constant.  Temperature and pressure rise.   Heating is stopped and the energy added to the system, which is proportional to C_V, is noted.

The piston is now freed and moves outwards, expanding without absorbing energy (adiabatic expansion).  Doing this work (proportional to C_P) cools the air to below its starting temperature.  To return to the starting temperature the air must be heated.  This extra heat amounts to about 40% of the previous amount. This article covers adiabatic processes in thermodynamics. ... Work (abbreviated W) is the energy transferred by a force to a moving object. ...

Thus air has an adiabatic index of approximately 1.41; a result often used in aerodynamics. Air is a name for the mixture of gases present in the Earths atmosphere. ... Aerodynamics is a branch of fluid dynamics concerned with the study of gas flows, first analysed by George Cayley in the 1800s. ...