Result: It is a geometric consequence of firing within a rotating, translating frame.
1. The Observed Fact
Long-range artillery shells fired north or south deflect east or west relative to Earth’s surface.
This effect is routinely attributed to a fictitious Coriolis force.
2. The Inertial Description
In an inertial frame, the projectile travels in a straight line at constant velocity after launch.
No lateral force acts on it.
3. The Moving Ground
The Earth rotates beneath the projectile during flight.
The launch point and target point are transported laterally while the projectile is in transit.
The projectile does not curve. The surface does.
4. Nested Transport Geometry
The observed trajectory is the difference between:
- straight-line inertial transport of the projectile
- rotational transport of the Earth frame
This mismatch produces apparent curvature.
5. Why Deflection Depends on Latitude
The local tangential velocity of Earth varies with latitude.
Shots fired poleward or equatorward inherit different lateral velocities than the ground beneath them.
No force is required — only relative transport.
6. Two Independent Derivations
Method A: Frame Transport
Compute projectile motion in an inertial frame, then subtract Earth’s rotation.
Method B: Energy–Inertia Accounting
The projectile conserves its initial tangential velocity while the ground does not.
Both predict identical deflection.
7. Why Coriolis Forces Were Invented
Freezing the Earth frame makes inertial motion appear curved.
Forces are then added to repair the description.
This preserves equations but inverts cause.
8. What the Effect Really Demonstrates
Coriolis deflection demonstrates that motion persists while frames move.
It is evidence for inertia, not force.
9. Transport-First Summary
The projectile does not curve.
The Earth does.
Forces are bookkeeping for frozen frames.