Gregory Rouan, age 13, of Struthers, Ohio, for his question:
What is the kinetic theory of gases?
Kinetic is coined from a Greek word for "motion" and motion is a form of energy we encounter very early in life. Scientists assume that kinetic energy is present in gases and other forms of matter. Its behavior is governed by precise laws involving temperature and pressure.
The alchemists of the Middle Ages dreamed of a concept called perpetual motion. They spent fruitless hours trying to devise a gadget with moving parts that would run indefinitely without fuel or any outside source of energy. True, we have not invented such an engine either. But we know that the frustrated alchemists could have created a working model of perpetual motion, merely by corking a flask of gases. But they did not know enough about the laws of physics, the science of matter and energy.
Most of these laws have been discovered in the past 400 years. The early experimenters used gases, though they were unaware that gases are widely separated units of matter. Imagine, for example, a space big enough to hold a pin head. If this volume is filled with gas, 9,999 parts of it are empty space. The remaining 1/1,OOOth part is occupied by enough separate molecules to far out number the world population, plus all the people of the past. These gaseous particles of matter separate and spread out evenly to occupy the entire available volume.
Charles Boyle did not know this in 1662 when he published his experiments in compressing, or squeezing gases. Boyle's Law states that when a volume of gas is decreased by half, its pressure is doubled. In 1786, Jacques Charles demonstrated that added temperature increases the volume of gases at a fixed ratio. Each degree of heat or cold causes a gas to expand or contract by the exact same amount of its original volume. In 1811, Amedo Avogadro demonstrated that the number of gas molecules, large or small, in a given volume is always the same, provided heat and pressure are the same.
By this time, scientists had accepted the idea that gases and other forms of matter are composed of individual atoms and molecules. They suspected that these units of matter exerted forces of attraction upon each other. The laws discovered earlier indicated that these bonds resist the influence of heat and pressure and led to the kinetic theory of gases. Atoms and molecules convert heat energy into the energy of motion. Widely separated gas molecules use heat to gain speed: Under normal conditions they zoom in all directions at speeds of about 115th of a mile per second and collide with their neighbors five billion or so times a second. These collisions, however, cause no loss of energy. The units of matter bounce off and zoom on their way in a flask of gases, or in the atmosphere outside it, for that matter, this kinetic activity continues to work as: long as there are molecules and some degree of heat. The old concept of perpetual motion was not, perhaps, too far from reality.
The kinetic theory is applied also to liquids and solids. In liquids, the bonds of attraction are weaker and kinetic energy allows them the freedom of slithering, flowing motions. In densely packed solids, the bonds of attraction freeze the units of matter into rigid lattice works. Modern X rays can photograph these crystal structures. And when the crystal is heated, the pictures blur, showing that tempera¬ture increases kinetic energy, even in the dense particles of solid materials.