The Slingshot Effect

The slingshot effect is used to accelerate a spacecraft in a planetary flyby.

NASA calls this a gravity assist, and exploits it to save fuel in missions to outer planets such as Jupiter and Saturn.

The planets continue in their orbits unaffected, and so at first sight this seems like something for nothing, a cosmic perpetual-motion trick.

But the physics is straightforward, resting only on conservation of momentum and of energy -- and involving the huge mass ratio between planet and spacecraft ...

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