Eötvös Effect: Introduction

Introduction Our planet rotates on its axis from the West to the East, which as many will recognize, creates horizontal deflection for bullets in flight, known as the Coriolis effect. Under the right conditions, this same rotation can also create a vertical deflection, becoming a relevant component of ballistic solutions assembled for top ranges. Variables When accounting for vertical Coriolis deflection (or the Eötvös effect), our latitude will have the same effects on the magnitude of deflection, but now direction will become a relevant variable too: When firing to the East, our bullet travels in the same direction as the planet spins. Although our projectile will begin to move independently from the rotation of the planet when it leaves our barrel, the target will not, still being firmly rooted to the Earth. As the bullet loses its velocity inherited from the planets’ rotation, but the target does not, the target will begin to move further away and lower (along the curvature of the earth) from our bullet in flight. This relative lowering of the target raises our point of impact. When firing towards the East, point of impact will be higher When firing to the West, the opposite is true. As our projectile flies against the rotation of the planet, the target will maintain its Eastward velocity, moving closer and higher (along the curvature of the earth) towards out bullet. This relative raising of the target lowers our point of impact. When firing towards the West, point of impact will be lower It should be noted that there will be no vertical deflection when firing directly North or South, as our target is only in relative motion from West to East as a product of global rotation. When firing either straight North or South, there will be no vertical deflection Between our Northern & Southern directions where there is no vertical deflection, and our Eastern & Western directions where we experience maximum vertical deflection, we have many scenarios in which our bullet will experience only a portion of the full deviation value. Relevance The Eötvös effect may best be classified as a tertiary consideration. Considering that human targets are much taller than they are wide - we are given enough flexibility in target rich environments to still meet great effectiveness without factoring for this additional variable. In high value target environments, or when shots are directed mostly to the East or West, the Eotvos effect can become an important variable to consider - potentially displacing a bullet by as much as horizontal Coriolis can at maximum values. In either instance, accounting for Eötvös can allow a greater degree of error in our ranging estimates without producing a miss, increasing hit probability should time permit.