• A diagram showing how propulsion works.
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    A diagram image of two red balloons, side-by-side above a large rocket engine. 

    The left balloon is tied shut, with arrows showing the air inside pushing equally against all sides. This balloon is labelled "equilibrium." 

    The right balloon has arrows pushing against each of the sides, and is untied on its right end, releasing air out. The release arrow is large and labeled "action" while the opposite direction, propelling the balloon, has a large arrow labeled "reaction." These words also have lines pointing to the same reaction happening in the rocket engine underneath.

  • A diagram showing how propulsion works.

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Smithsonian's National Air and Space Museum

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Smithsonian Institution

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