`g_"earth" = 9.80665 m/s^2`

-9.80665

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`.

The Math / Science

The acceleration due to gravity can be computed in the following formula:

           g = (G•M)/R²

Where:

• g is the acceleration due to gravity.
• G is the Universal Gravitational Constant (G)
• M is the mass of the object (e.g. planet)
• R is the distance to the center of mass of the object (Earth radius in this case).

Ballistic Flight Calculators

• Ballistic Max Range:  This is the maximum horizontal range.
• Ballistic Max Height:  This is the maximum altitude in free ballistic flight.
• Ballistic Travel Time:  This is the time duration of free flight.
• Velocity to Achieve Max Height: This computes the initial velocity at a launch angle needed to reach a max height.
• Initial Horizontal Velocity: This is horizontal velocity or ground speed.
• Initial Vertical Velocity: This is the vertical velocity at a given time.
• Ballistic Position at Time (t): This compute the position (x,y) at a given time within ballistic flight, where x is distance down range and y is the height above the plane.
• Ballistic Parabolic Equation provides the parabolic flight position equation based on the launch speed, height and angle.
• Acceleration Due to Gravity at Sea Level