Air has weight and exerts a pressure of 10 N/cm2 (or 14.7 lbs/in2) at sea level. Gases are not “no thing.” Gases have mass, occupy space, exert pressure, and are composed of molecules separated by truly “empty” space. Inertia, or the tendency of a body at rest to stay at rest, is also a relevant factor in this experiment. This free selection includes the Table of Contents, Introduction, a Science Education Topics section, and the Index.