Newton's cannonball

A cannon on top of a very high mountain shoots a cannonball horizontally. If the speed is low, the cannonball quickly falls back to Earth (A, B). At intermediate speeds, it will revolve around Earth along an elliptical orbit (C, D). Beyond the escape velocity, it will leave the Earth without returning (E).

Newton's cannonball was a thought experiment Isaac Newton used to hypothesize that the force of gravity was universal, and it was the key force for planetary motion. It appeared in his posthumously published 1728 work De mundi systemate (also published in English as A Treatise of the System of the World).[1][2]

  1. ^ De mundi systemate, Isaac Newton, London: J. Tonson, J. Osborn, & T. Longman, 1728.
  2. ^ A Treatise of the System of the World, Isaac Newton, London: printed for F. Fayram, 1728.