PRINCIPAL

    There are many everyday examples of jet propulsion. A blown-up toy balloon with its neck closed shows no tendency to move because the air inside is pressing equally in all directions. If the neck is opened suddenly, the balloon shoots away. The escaping air relieves pressure at the neck, and there is a reaction from the air opposite the neck. It is not the air rushing out of the neck and pushing against the outside air, however, that drives the balloon ahead. It is the air pushing against the inside front wall of the balloon that propels it forward. In fact, a jet would operate more efficiently in a vacuum because there would be no air to obstruct the escaping gasses.

    The recoil of a rifle also illustrates action and reaction. Expanding gasses propel the bullet out of the barrel at high velocity. The rifle in response to the force of the gasses "kicks back." Another example of jet action is the garden hose whose nozzle jumps back when the water is suddenly turned on full force.

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