At such a minute scale, everyday forces such as gravity are not the main obstacles to be overcome.

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His main characters include G, the strength of gravity, h, Planck's constant, which governs the quantum nature of reality at small scales, e, the charge of the electron, and c, the speed of light itself.

ECONOMIST: Modern physics

The gravity assist would allow a safe return to Earth even if the spacecraft's main rocket engine failed, Professor Longuski said.

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It was once thought that asteroids in the main belt occasionally collided with one another, sending fragments into orbital resonance bands where they could be affected by the gravity of Jupiter or Saturn.

ECONOMIST: Celestial mechanics: A rock in a hard place | The