ReadonlyaccelerationConstant acceleration.
ReadonlydurationBallistic flight time: the time at which the path returns to the plane
through from perpendicular to acceleration, i.e.
-2 · (v₀ · â) / |a|.
For the usual case — launched upward under gravity — this is the familiar
2 · v₀ᵧ / 9.81, and duration / 2 is the apex. It is Infinity when the
path never returns (zero acceleration, or an initial velocity with no
component opposing the acceleration), because there is no other honest
answer; pass duration explicitly for a fixed preview window.
ReadonlyfromPosition at time = 0.
ReadonlyinitialVelocity at time = 0.
§13's "ballistic" trajectory: ParabolicTrajectory with
accelerationdefaulted to gravity(0, -9.81, 0)(Appendix A, Y-up per §7a). Everything else — sampling, extrapolation, the derived flight-timeduration— is inherited unchanged.