The motion of a projectile can be completely described in terms of ...
- the direction in which it is launched
- its speed at launch
- the local acceleration of gravity
plus, if air resistance is to be taken into account ...
- the projectile's size, shape, weight, mass distribution, composition, and surface texture
- the temperature, pressure, humidity, wind speed, and turbulence parameters
of the air it encounters at every point in its trajectory.
That's why air resistance is always ignored for simple exercises in projectile motion.
