Tension is the force which a gas always exerts when confined to a limited space. In the example, a partially filled football is placed in a glass jar (a receiver) from which air has been exhausted. The football immediately expands. This experiment also works with a bladder. A branch of mechanics that deals with the properties of gases is called pneumatics.
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International Correspondence Schools A Textbook on Mechanical and Electrical Engineering (Scranton, PA: International Textbook Company, 1897)