When simulating an airplane and a missile, to get them moving in the air we apply a force in one direction. Now an airplane has wings that keeps it afloat while a missile can have fins to stabilize it. In both cases when the force is no longer strong enough, the velocity reduces and the projectiles are bound to succumb to gravity. When that happens, the projectiles naturally don't fall directly to the ground disregarding rotation and other spins based on air resistance and whatever momentum there is left.
- Gravitational pull and momentum acting on the projectiles.
- Air resistance acting on the projectiles.
- Both 1 and 2 above's behavior can be based on varied levels of a central forward force applied on the projectiles.