Gas is one of the four fundamental states of matter. The others are solid, liquid, and plasma. 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. A gas mixture, such as air, contains a variety of pure gases. What distinguishes gases from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colorless gas invisible to the human observer.
Drifting smoke particles indicate 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.
Boyle's equipment
In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma. Many intermediate states are known to exist, such as liquid crystal, and some states only exist under extreme conditions, such as Bose–Einstein condensates and Fermionic condensates, neutron-degenerate matter, and quark–gluon plasma. For a list of exotic states of matter, see the article List of states of matter.
Bromine in both liquid and gas state, encased inside acrylic in solid state
Helium's orange glow in its plasma state
Artificial plasma produced in air by a Jacob's Ladder. The extremely strong potential difference between the two rods ionize particles in the air, creating a plasma.
SBS block copolymer in TEM
