projectile is an object upon which only the force of gravity is acting. For our discussions we assume that the influence of air resistance can be neglected.
For example, an object dropped from rest at some height is a projectile as long as it is in the air.
Generally, the projectile is an object thrown into the air:
vertically upward or downward,
horizontally,
or at any angle to the Earth surface.
In Physics we will study here the motion of a projectile, its velocity, acceleration, displacement, and trajectory, that is the path drawn by a moving projectile. As already mentioned we neglect air resistance.
We must be aware that equations presented in this paragraph will be true for projectiles such as a small stone, metal ball from a ball bearing, or a small ball from heavy plastic. A feather or sheet of paper will not move as a projectile because the friction due to presence of air is too large to be neglected.
The free fall motion from Chapter 1. p. 5 is a special case (one dimensional) of a projectile motion. Here we start with a quite general, classical case of a projectile motion. The situation for deriving equations is depicted in Fig. M2.3.