Answer :

markopolo
lets take a bow and arrow 4 example
u shoot it
the arrow goes 30 feet and then it hits the ground because of gravity
without gravity...the arrow would go forevermore onward
AL2006
Gravity has no effect on horizontal motion, but it causes accelerated vertical motion downward. 

The result of this combination is that if the projectile is launched with ANY
horizontal motion ... not straight up or straight down ... then its motion from
the time it's launched until the time it hits the ground is always a part of a parabola.

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