This constant represents the acceleration due to gravity (g) at sea level on Earth in meters per second squared (`m/s^2`) as it is used in the modeling of projectile motion.
If we decompose the projectile motion into an x-component and y-component model, the y-component of acceleration for a projectile is the negative of the gravitational acceleration due to the Earth's mass. It consequently has to be represented as a negative acceleration contributing to a downward force on an object (in the negative y direction).
This simplified model assumes no acceleration component due to other forces, such as air friction, so drag should be computed separately in an expansion of this model. Likewise, the x-component acceleration, in a model neglecting air resistance would be: `a_x = 0`.