As Robert told us a projectile is an object that moves through the air or through space, acted on only by gravity (and air resistance, if any). When you through a ball it will fall to the ground because of the gravity that is acting on it. Without gravity the ball's path would be a straight horizontal line. If you could throw a ball so fast that the curvature of the earth would come into the picture, what would happen? Well, the ball follows a curved downward path and the earth is curved, so if the ball was thrown fast enough to clear the horizon, with no air resistance, it would orbit the earth. This is what an earth satellite or space shuttle is. A satellite is a projectile that's traveling so fast, that it is falling around the earth rather than into it. Bits of rock and other meteorites that graze the earth's atmosphere are also fast moving projectiles that burn up and to us look like "falling stars." -Love, Kristi