I have not seen an article on the lateral deflection caused by the Coriolis Effect that takes into account the direction in which a person is shooting. I read the article that notes the elevation differential but it doesn’t mention the lateral displacement.
Logic tells me that if I was shooting either due east or due west. the lateral deflection would be zero. Conversely, shooting north or south, the deflection would be maximized. Therefore, doesn’t one have to know the direction in which he is shooting in order to adjust for both the vertical and lateral adjustments that should be made to allow for the Coriolis effect?
Most of my shooting is at or less than 500 yards so I don’t normally consider the effects of the earth’s rotation. The wind is usually my biggest concern.
If the only force on your bullet is gravity (e.g., the Earth stopped spinning before you took your shot), then the bullet would follow a great circle (NOT your line of latitude unless you’re on the equator). When you take into account the effects of a rotating frame of reference (Coriolis effect for one), the path gets even weirder. See here.
Well, let’s see. Googling the first site that purports to tell me how long it takes a rifle-fired bullet to travel 500 yards, I get 0.741 seconds.
To simplify the math, let’s imagine shooting a rifle from the North Pole. The target rotates (very close to) 1000*PI yards = 113,097 inches in a day, or just about an inch in 0.741 seconds.
At lower latitudes, the deflection due to differential rotation would be . . . something less than an inch.
I’m not sure at what point deflection begins to matter. I suppose it depends on how good a shooter you are.
Yeah, if you gave me a muzzle velocity I could run the calculations like I did in the thread Leo Bloom linked to. Note, however, that for a given distance of travel, the amount of deflection due to the Coriolis force is inversely proportional to the velocity. The magnitude of the acceleration is directly proportional to the velocity, but the time-of-flight over which it acts is inversely proportional to the velocity of the projectile, and the total deflection is proportional to (acceleration)*(time)[sup]2[/sup].
As far as the direction of the deflection goes, to a pretty good approximation that’s going to be at right angles to the direction of the bullet’s flight and to the earth’s axis of rotation. This can be split into a horizontal deflection that will be a constant amount of deflection to the right relative to a straight line, independent of the direction of fire; and a vertical deflection that will vary depending on the direction of fire (it’ll be zero when firing due north or south, and maximized when firing due east or west.)
This has already been answered, but just to clarify: this is true only if you’re shooting at the equator. Also, it applies to any direction, but of course, if you’re not shooting due east or west, then the bullet leaves the equator.
In the northern hemisphere, deflection is to the left. In the southern, it’s to the right. The effect is greatest at the poles and diminishes toward the equator, where it’s zero.
Whenever I get confused trying to work it out, one of the tricks I use is to get rid of one dimension, and think of a spinning disk (like an LP), and imagine moving on the spinning surface. It’s a lot easier to visualize, and captures the spirit if not all the details of the effect. For an example of a detail that disappears, on the spinning disk, there is no equator, only one of the poles. (It’s an excellent approximation of the effect at or very close to the poles.)
Imagine people growing up on a spinning spacecraft, with multiple levels and even a chamber that’s open all the way “up” – that is, a big cylindrical room. These people would have a great intuitive understanding of the effect! Imagine passing a ball in that cylindrical room. Normally, the Coriolis effect is constrained to the surface of the sphere. In this case, it wouldn’t be, and we’d also see the vertical aspect, just as we’d see for a bullet.
One of the ballistic apps I have on my phone has an input field for direction of aim. It already knows location through GPS. There’s a button to enable or disable Coriolis Effect, but I’ve never played with it.