A projectile is launched from the origin at an angle ϕ 0 with the horizontal; the subsequent position is given by (t). For small enough angles the distance from the origin r = However, increases. However, if a projectile is launched nearly straight up it rises to a highest point, and then moves back toward the origin, so that the distance to the origin first increases then decreases. What initial launch angle ϕc divides the two types of motion? (See"Projectiles: Are They Corning or Going?," by James S. Walker, The Physics Teacher; May 1995, p. 282.)

A projectile is launched from the origin at an angle ϕ₀ with the horizontal; the subsequent position is given by (t). For small enough angles the distance from the origin r =  However, increases. However, if a projectile is launched nearly straight up it rises to a highest point, and then moves back toward the origin, so that the distance to the origin first increases then decreases. What initial launch angle ϕc divides the two types of motion? (See"Projectiles: Are They Corning or Going?," by James S. Walker, The Physics Teacher; May 1995, p. 282.)