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# Coriolis effect

#8
11-08-2003, 08:17 PM
 Silver Member Join Date: Dec 2002 Posts: 374
Re: Coriolis effect

Refering to the Ohio St U Physics Dept there is an example that actually even refers to artillery projectiles in section 3.1. This explaination is contrary to Dave's. My guess on this conclusion, though it is not mentioned specifically, is that in addition to the eastward velocity component, there must also be an acceleration due to yaw during rotation of the origin. The yaw, independant of the eastward velocity (they always use east in the example) is going to produce a lateral velocity that, relatively speaking will increase as it nears the equator, reducing the effect of the southward shots "right hand" motion. Conversely, it also reduces the apparent eastward velocity when fired northward.

I guess another way to think of it is, those velocities would only be unaffected if you fired the shot dead verticle at which time the projectile would act like a geo-synchronous sattelite and fall right back on the shooter. It would continue to rotate at exactly the same speed as the earth, then gravity would set in and bring it straight back down to the same spot. (regardless of the latitude)
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If you have something that you disassemble and reassemble enough times, sooner or later, you'll have two!
#9
11-08-2003, 08:30 PM
 Silver Member Join Date: Dec 2002 Posts: 374
Re: Coriolis effect

Ohio St U, Coriolis explaination.
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If you have something that you disassemble and reassemble enough times, sooner or later, you'll have two!
#10
11-08-2003, 09:03 PM
 Platinum Member Join Date: May 2001 Posts: 2,369
Re: Coriolis effect

4mesh063

In reference to section 3.1 in the article

"3.1. I Feel The Earth Move Under My Feet: North/South Motion
Note first that all points on the Earth have the same rotational velocity, w (they go around once per day). Also, places at different latitudes have different linear speeds. A point near the equator may go around a thousand miles in an hour, while one near the North Pole could be moving only a few dozen miles in an hour.
Normally, objects in contact with the ground travel the same speed as the ground they stand on. As a result, the Coriolis force generally doesn't have a noticeable effect to people on the ground; the speed of the point you're standing on and the speed of the point you're stepping onto are too close for you to tell the difference. Or, looking back at the Coriolis Force equation above, if the velocity relative to the rotating frame (the Earth) is zero, so is the Coriolis force.
However, when an object moves north or south and is not firmly connected to the ground (air, artillery fire, etc), then it maintains its initial eastward speed as it moves. This is just an application of Newton's First Law. An object moving east continues going east at that speed (both direction and magnitude remain the same) until something exerts a force on it to change its velocity. Objects launched to the north from the equator retain the eastward component of velocity of other objects sitting at the equator. But if they travel far enough away from the equator, they will no longer be going east at the same speed as the ground beneath them.
The result is that an object traveling away from the equator will eventually be heading east faster than the ground below it and will seem to be forced east by some mysterious force. Objects traveling towards the equator will eventually be going more slowly than the ground beneath them and will seem to be forced west."

I do not see this as contrary to my statement(s) perhaps I explained poorly and/or there was an interpretion problem. As in my statement(s), both target and origin site have eastward but dissimilar speeds. If the speed of the target is less than the speed of the origin site ( a northerly shot in the northern hemisphere) the projectile will be deflected to the east and if the target has greater eastward speed than the origin site the projectile will be deflected to the west (a southerly shot in the northern hemishpere). Whether the varying shot deflection is eastward or westward it's always to the right for Coriolis in the northern hemisphere.
#11
11-08-2003, 10:03 PM
 Platinum Member Join Date: Jun 2001 Location: Palmer, Alaska Posts: 2,539
Re: Coriolis effect

Phil,
The way I understood Dave's explanation and the article you posted the link to, which Dave pasted above, says the same thing?

POI will always be to the right in the northern, and to the left in the southern hemisphere.

The result is that an object traveling away from the equator will eventually be heading east faster than the ground below it and will seem to be forced east by some mysterious force. Objects traveling towards the equator will eventually be going more slowly than the ground beneath them and will seem to be forced west."

Now, I'll bet it has a varying degree of deviation depending on what latitude you're shooting from as well. In the same hemisphere and shooting the same direction and the same distance that is...
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Brent Moffitt
#12
11-08-2003, 10:34 PM
 Gold Member Join Date: Sep 2002 Location: Illinois Posts: 837
Re: Coriolis effect

A...let me see if I understand the practical application of this...If I'm North of the Equator and am shooting North, then I should use a left hand twist bbl to counter this effect. And if shooting South being South of the Equator a right hand twist, correct? But what happens if I fire one off say Northeast or Southwest? I guess I'll have to take a compas reading and choose the rifle with the proper twist. [img]images/icons/confused.gif[/img] [img]images/icons/confused.gif[/img] [img]images/icons/confused.gif[/img]
Good shooting,
db
#13
11-09-2003, 06:30 AM
 Platinum Member Join Date: May 2001 Location: Lock Haven P.A. Posts: 1,071
Re: Coriolis effect

You guys have "WAY TO MUCH TIME ON YOUR HANDS" [img]images/icons/grin.gif[/img]
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Boyd Heaton...
#14
11-09-2003, 08:23 AM
 Platinum Member Join Date: May 2001 Location: Pennsylvania Posts: 1,757
Re: Coriolis effect

Hello fellows.

As I have mentioned before, thats why when LR hunting, "we" take a "sighter shot" first. [img]images/icons/grin.gif[/img] [img]images/icons/grin.gif[/img]

It will eliminate the variables such as rotation speed of the earth, direction we are shooting and the wind, all in one operation. No need to worry about the long math equasions , just the elevation and windage knobs and how they effect the impact of the bullet from point A to point B.

Since we are not putting a rocket into orbit or going to the moon or shooting 1000 miles or more with a projectile, the sighter shot method leaves more time to enjoy our hunting and allows clean kills in the process.

Speaking of enjoy, I have to go send a few bullets across the mountains today out to 1500 to 1800 yards.

I try to keep it simple and it has always Worked for me.

Later
DC
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Darryl Cassel

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