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The information below is intended to provide introductory material for elementary students and further material for high school students.

Please keep in mind that not all demonstrations are presented at each show, and each topic may not be covered.



  • A gas exerts pressure on all sides of the container which holds the gas. The amount of pressure is related to the energy of the gas and the amount of gas. The higher the energy, the more pressure is exerted, and the more gas is contained, the more pressure is exerted.

    Gases expand to fill the boundaries of their containers. Once a gas has filled the container, it keeps pressing outwards, continuously trying to expand. This expansion creates a pressure on the sides of the container. The pressure is exerted by the molecules of the gas colliding with the sides of the container. The more energy a gas has, the more energy its molecules will have, and the more pressure will therefore be exerted. If there is more gas inside a given container, there will be a higher number of average collisions with the sides of the container, and more pressure will therefore be exerted.

    A container may be of any size and shape. A common container of air is a balloon. Another container of gas is the Earth's atmosphere: the gas inside the Earth's atmosphere is constantly pushing against the sides of its container (including you!). Due to the gas contained in the atmosphere, we are all constantly under a pressure of about fifteen pounds per square inch.

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    Related Demos

    The following demonstrations illustrate this physics topic:

    Sponsored by the Physics Department and the Center for Science, Mathematics, and Engineering Education -- University of Virginia