““A measure of the strength of a body's gravity is the speed with which a projectile must be fired to escape its grasp. It takes 11.2 kilometers per second to escape from the Earth. This speed is tiny compared with that of light, 300,000 kilometers per second, but it challenges rocket engineers constrained to use chemical fuel, which converts only a billionth of its so-called mass 'rest-mass energy' (Einstein's mc^2) into effective power. The escape velocity from the sun's surface is 600 kilometers per second-still only one fifth of one percent of the speed of light.””
