In the rotating reference frame of the Earth, a projectile in flight feels an apparent sideways force — the Coriolis force:
F_c = 2m(ω × v)
For a shell fired mostly horizontally, the sideways acceleration works out to a = 2ωv⋅sin(φ), where ω ≈ 7.29×10⁻⁵ rad/s is Earth's angular velocity, v is the shell's speed and φ is the latitude. Integrating that acceleration over the flight time T gives the classic estimate used in artillery firing tables:
Δx = 2ωv₀sin(φ)T²
- Latitude — sets sin(φ): zero at the equator, maximum at the poles. North of the equator shells drift right of the aim point; south of it, left.
- Muzzle velocity & launch angle — set the shell's speed and flight time T via standard projectile motion (gravity g = 9.8 m/s², no air drag).
- Effect exaggeration — for short, fast, direct-fire shots the true deflection is only centimetres and invisible at 1×; for the long, high-arcing shots this sim favours it can already reach tens or hundreds of metres. Either way the slider scales the drawn curve for clarity (auto-capped so it never flies off the stage) — the "real" stat box always shows the true, unscaled value.
The dashed grey line is the reference path a non-rotating observer would predict; the solid orange path is what actually lands — the gap between the two impact points is the Coriolis deflection.