conceptual notions about projectiles

* a projectile is any object upon which the only force is gravity,

* projectiles travel with a parabolic trajectory due to the influence of gravity,

* there are no horizontal forces acting upon projectiles and thus no horizontal acceleration,

* the horizontal velocity of a projectile is constant (never changing in value),

* there is a vertical acceleration caused by gravity; its value is 9.8 m/s/s, down,

* the vertical velocity of a projectile changes by 9.8 m/s each second,

* the horizontal motion of a projectile is independent of its vertical motion.