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PRINCIPLES OP GUNNERY. 
striking The striking velocity of a projectile is the velocity which it has on 
ve oci y. - m p ac k 
veiocit ntal -^e horizontal velocity of a projectile is its velocity at any point 
veoci 7 ' resolved in a horizontal direction. 
Vertical The vertical velocity of a projectile is its velocity at any point 
velocity. reso } ve( j a vertical direction. Thus, if V be the velocity of a pro¬ 
jectile moving at an angle a to the horizon, 
Horizontal velocity = V cos a, 
Vertical „ == V sin a. 
Gravity. Gravity is that force (caused by the attraction of the earth) 
which continually decreases the vertical velocity of the projectile in 
its ascending path, and then brings the projectile to rest in a vertical 
direction. Gravity then causes it to descend, and continually increases 
its descending vertical velocity till it strikes the ground. 
Thus, if OF be the line of fire, a the angle of fire, and V the muzzle 
velocity of a projectile, its ascending vertical velocity will be 
V sin a ; 
or if V = 650 f.s., and a = 30, 
ascending vertical velocity = 650 x ^ = 325 f.s. 
Gravity, and retardation due to the resistance of the air, combine to 
bring the projectile to rest at some point, A, if it were projected 
vertically upwards; but owing to the horizontal velocity of the pro¬ 
jectile, it will have moved on at the same time to the point P, which 
is called the vertex, or maximum height , of the trajectory. Then the 
projectile commences to fall, and acquires a descending vertical velocity 
(under the influence of gravity less the retardation due to the resistance 
of the air), which gradually increases till the projectile strikes the 
ground. The horizontal velocity meanwhile has carried the projectile 
to the point B. 
But when a projectile is fired at a high angle of elevation with 
considerable muzzle velocity, and consequently has a long vertical 
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