Horizontal projectile

In astronomy, geography, and related sciences and contexts, a direction or plane passing by a given point is said to be vertical if it contains the local gravity direction at that point.

Conversely, a direction or plane is said to be horizontal if it is perpendicular to the vertical direction.
In general, something that is vertical can be drawn from up to down (or down to up), such as the y-axis in the Cartesian coordinate system.

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