Portal:Gravitation/The effects of gravity
Newton conceived of gravitation when he considered the trajectory of a projectile . A projectile under the influence of gravity travels along a trajectory that is a conic section. The projectile follows either an elliptical path or a hyperbolic path, depending on whether its total mechanical energy is less than or greater than that necessary for escape velocity, respectively. In the pathological case where the projectile's total mechanic energy is exactly equal to that necessary for escape velocity, the projectile follows a parabolic trajectory. At low speeds and over small distances (small enough that the surface of the Earth can be considered flat), the elliptical trajectory of a projectile can be more easily approximated as a parabolic trajectory.
When Newton heard the sound of an apple falling on the ground, he asked himself might the same cause (which he called gravitation) for the motion of the apple, also explain the motion of the moon?. This was the first statement of the universal law of gravitation.
