A projectile is an object upon which the only force acting is gravity. There are a variety of examples of projectiles: an object dropped from rest is a projectile (provided that the influence of air resistance is negligible), an object thrown vertically upwards is a projectile (provided that the influence of air resistance is negligible), and an object thrown upwards at an angle is also a projectile (the same assumption). A projectile is any object which, once projected, continues its motion by its own inertia and is influenced only by the downward force of gravity.

By definition, a projectile has only one force acting upon - the force of gravity. If there were any other force acting upon an object, then that object would not be a projectile. Projectiles can be launched both horizontally and vertically, and they have both horizontal and vertical velocity and horizontal and vertical displacement.