A projectile is any object that is given an initial velocity and follows a path determined by the effects of gravitational acceleration and air resistance. Projectile motion is the act of projecting an object into the air at an angle when a curved path is an object follows when thrown or propelled near the surface of the earth. For example: a thrown football, an object dropped from an airplane, or a bullet shot from a gun. Projectile motion may only be used to solve mechanics problems if the acceleration is constant.
The path followed by a projectile is called its trajectory. It is affected by gravity. We shall neglect the effect of air resistance and the curvature and the rotation of the earth when we want to analyses projectile motion. Projectile motion is always confined to a vertical plane determined by the direction of the initial velocity. This is because the acceleration due to gravity, g is always vertically downwards and hence has no effect on the horizontal motion of the projectile. Thus projectile motion is two-dimensional motion.
We can consider the plane of plane of motion as the x- coordinate and y- coordinate with the x-axis horizontal and the y-axis vertically upward. In another words, projectile motion can be resolved into two perpendicular component: a horizontal component with constant velocity (zero acceleration)and a vertical component with constant acceleration,g (free fall) We can analyses projectile motion as a combination of Horizontal motion with constant velocity and vertical motion With constant acceleration.