Ballistics
External ballistics studies the trajectory of a projectile when it is outside of the object which accelerates it (such as when a bullet leaves the barrel of the gun, from which it is fired). This trajectory depends on three ballistic conditions - the beginning speed, the angle at which the object is thrown, and the ballistic coefficient (a number, which describes the influences of the air on the object). Trajectory of a projectile is also influenced by (depends on) resistance of air, rotation of bullet, the density and pressure of the air, and the strength and direction in which the wind may be blowing. For long-distance missiles, they also have to consider the changes in the magnetic field of the Earth.