Shooting Science: The Coriolis Effect Explained
The Coriolis Effect comes into play with extreme long-range shots like this. The rotation of the earth actually moves the target a small distance (in space) during the course of the bullet’s flight. Photo by Dustin Ellermann at Whittington Center Range.
When you’re out at the range, the Earth seems very stable. But it is actually a big sphere zooming through space while spinning around its axis, one complete turn every 24 hours. The rotation of the earth can create problems for extreme long-range shooters. During extended bullet flight times, the rotation of the planet causes an apparent deflection of the bullet path over very long distances. This is the ballistics manifestation of the Coriolis Effect.
Bryan Litz of Applied Ballistics has produced a short video that explains the Coriolis Effect. Bryan notes that Coriolis is “a very subtle effect. People like to make more of it than it is because it seems mysterious.” In most common shooting situations inside 1K, Coriolis is not important. At 1000 yards, the Effect represents less than one click (for most cartridge types). Even well past 1000 yards, in windy conditions, the Coriolis Effect may well be “lost in the noise”. But in very calm conditions, when shooting at extreme ranges, Bryan says you can benefit from adjusting your ballistics solution for Coriolis.
Bryan explains: “The Coriolis Effect… has to do with the spin of the earth. You are basically shooting from one point to another on a rotating sphere, in an inertial reference frame. The consequence of that is that, if the flight time of the bullet gets significantly long, the bullet can have an apparent drift from its intended target. The amount [of apparent drift] is very small — it depends on your latitude and azimuth of fire on the planet.”
Coriolis is a very subtle effect. With typical bullet BCs and velocities, you must get to at least 1000 yards before Coriolis amounts to even one click. Accordingly, Bryan advises: “Coriolis Effect is NOT something to think about on moving targets, it is NOT something to think about in high, uncertain wind environments because there are variables that are dominating your uncertainty picture, and the Coriolis will distract you more than the correction is worth.”
“Where you could think about Coriolis, and have it be a major impact on your hit percentage, is if you are shooting at extended range, at relatively small targets, in low-wind conditions. Where you know your muzzle velocity and BC very well, [and there are] pristine conditions, that’s where you’re going to see Coriolis creep in. You’ll receive more refinement and accuracy in your ballistics solutions if you account for Coriolis on those types of shots. But in most practical long-range shooting situations, Coriolis is NOT important. What IS important is to understand is when you should think about it and when you shouldn’t, i.e. when applying it will matter and when it won’t.”
The Coriolis Effect — General Physics
The Coriolis Effect is the apparent deflection of moving objects when the motion is described relative to a rotating reference frame. The Coriolis force acts in a direction perpendicular to the rotation axis and to the velocity of the body in the rotating frame and is proportional to the object’s speed in the rotating frame.A commonly encountered rotating reference frame is the Earth. The Coriolis effect is caused by the rotation of the Earth and the inertia of the mass experiencing the effect. Because the Earth completes only one rotation per day, the Coriolis force is quite small, and its effects generally become noticeable only for motions occurring over large distances and long periods of time. This force causes moving objects on the surface of the Earth to be deflected to the right (with respect to the direction of travel) in the Northern Hemisphere and to the left in the Southern Hemisphere. The horizontal deflection effect is greater near the poles and smallest at the equator, since the rate of change in the diameter of the circles of latitude when travelling north or south, increases the closer the object is to the poles. (Source: Wikipedia)
Similar Posts:
- Shooting on a Spinning Planet — The Coriolis Effect
- Extreme Long Range: Understanding the Coriolis Effect
- Shooting on a Spinning Planet — Explaining the Coriolis Effect
- Long Range Shooting on a Spinning Planet — The Coriolis Effect
- Saturday at the Movies: Litz on Long Range Shooting + Ballistics
Tags: ballistics, Bryan Litz, Coriolis Effect, Deflection, Earth Rotation, ELR, Inertia, Long-Range
Photo credit: Dustin Ellermann
Tried the shooters app for 10$, tried to open, did not, tried again, and again, then read the reviews, THEN asked for a refund……not a good track record so far.
I do need a good, better, best shooters program and would love to find one, but if it won’t open, it’s no good to this beginner.
Instructive video from MIT showing a simple demo of coriolis effect:
https://youtu.be/dt_XJp77-mk
Found another video explaining spin drift:
https://youtu.be/ty9QSiVC2g0
I recommend that everyone with the slightest interest in this subject as it elates to shooting, click on the link that Steve has been so kind to provide. The demonstration is excellent and quite straightforward. Anyone can readily understand it. Once it has sunk in, I suggest that you consider that this is really two related subjects, one about global wind patters, and the other about external ballistics. Unfortunately statements that are true about the former, seem to have been widely misconstrued to apply to the latter. As one approaches the poles, the rotational speed of a point on the surface decreases to the point where at either pole, it is zero, and it is that speed that is proportional to the amount of corilois drift that a long range shot would have to compensate for. If the shot is fired toward the north pole, and the target is not at the pole, the bullet would strike to the left, but if we think about it for a moment, visualizing what happening, if the direction of the shot is reversed, starting where the initial target was and going to the original firing line, from the perspective of the shooter, who is facing south, the bullet is deflected to the right. Also, if one fires parallel to the rotation in the same direction (west to east) the point of impact would be above the point of aim. The opposite would be true if the direction of the shot were reversed. shots fired at various headings neither parallel with the equator or toward a pole would be affected by the sum of these two effects, which would show as bullets impacting some distance diagonally from their points of aim. Again, what we seem to have here is large scale misapplication of statements made about global wind patters, and how they are generated, and external ballistics, but given the wide disparities in readers abilities to visualize, it is likely to continue unabated.