Temperature is the average rate of motion of the atoms or molecules contained in a fluid medium.
The different rates at which collective molecular motions occur determine the various states of gas, liquids, and solids.
A molecule travels at a speed which is inversely proportional to its mass and density, and depends upon the number, kind, and arrangement of its atoms, and the forces which influence it.
The lightest molecules, containing atoms with the fewest electrons and nucleons, travel at the fastest speed and correspond to the highest temperature. The heaviest molecules travel at the slowest speed and correspond to the lowest temperature.
Light hydrogen molecules travel at about 1 mile per second in normal air, while heavy mercury vapor travels at about one-tenth of a mile per second.
Pressure is the collective outward force of molecular motion.
Low pressure produces a slow rate of molecular activity and a cool temperature. High pressure produces a fast rate of activity and a warm temperature.
The least occurrence of molecular motion in a fluid medium causes extreme rigidity as it approaches temperatures of nearly absolute zero.
Absolute zero is a non-demonstrable state of complete rest which corresponds to a temperature of minus 273 degrees centigrade, zero degrees Kelvin.
The first one-thousandth of one degree above absolute zero gives simple molecules, on the average, enough momentum to travel a few centimeters. An increase of only a few thousandths of a degree produces a normal interaction of molecular activity.
With them who stood upon the brink of the great gulf which none can see beyond, Time, so soon to lose itself in vast Eternity, rolled on like a mighty river, swollen and rapid as it nears the sea. – Charles Dickens