Gas is one of the four fundamental states of matter. A pure gas may be made up of individual atoms, elemental molecules made from one type of atom, or compound molecules made from a variety of atoms (e.g. carbon …
Drifting smoke particles provide clues to the movement of the surrounding gas.
Shuttle imagery of re-entry phase
21 April 1990 eruption of Mount Redoubt, Alaska, illustrating real gases not in thermodynamic equilibrium.