Is it ensure, insure, or assure?
gravitation grav·i·ta·tion (grāv'ĭ-tā'shən)
The natural phenomenon of attraction between massive bodies.
The act or process of moving under the influence of this attraction.
A movement toward a source of attraction.
The force, first described mathematically by Isaac Newton, whereby any two objects in the universe are attracted toward each other. Gravitation holds the moon in orbit around the Earth, the planets in orbit around the sun, and the sun in the Milky Way. It also accounts for the fall of objects released near the surface of the Earth. The modern theory of gravitation is the general theory of relativity.