Sniping and Earth's Rotation

I saw a TV program recently where they demonstrated a fancy new sniper rifle with amazing range (a few km, can’t remember exactly), they said it came with a handheld computer to calculate the shot. The computer took all the influencing factors into consideration; windspeed, distance, etc. and rotation of the Earth ? They gave an example of shooting at the equator being different to shooting in NY.

How can the Earth’s rotation affect the shot ?

Google “Coriolis Effect.” It also affect weather patterns.

The Master addressed this topic here:

http://www.straightdope.com/columns/read/2944/how-does-the-earths-rotation-affect-the-path-of-a-bullet

And there was a good thread on this topic from about a year ago.

http://boards.straightdope.com/sdmb/showthread.php?t=568406&highlight=sniper+rifle+earth+rotation

Cecil had a column about this: How does the earth’s rotation affect the path of a bullet? (June 25, 2010)

There were also a few threads in CCC based on that column, the longest of which was Snipers and the Coriolis effect, but also How does the earth’s rotation affect the path of a bullet? and Bullet drop and the Coriolis effect.

Battleship fire control systems from the 1900s were designed to account for the coriolis effect. As they were firing over much greater distances than a sniper rifle the effect was much more pronounced.

It’s the rotational component of the motion that’s the problem - the bullet acquires a vector component equivalent to the momentary local movement of the earth’s surface as it exits the gun, but by the time (and place) it hits the target, everything has rotated a bit, meaning it’s moving in a subtly different direction, as it goes around.

I realise the above is just a really shoddy description of what the Coriolis effect is - I actually wanted to post to point out that if the experiment took place on a really vast flat treadmill (as opposed to the surface of a rotating spheroid), the effect would not occur at all, because target and gun would be affected by the same constant vector.

I remember way back when I took Mechanics 1 in college. When you set up the math to describe the motion in an “on a rotating planet” scenario and then crunch the math the coriolos effect just falls out. And IIRC the math wasnt too hard either. This was one of the situations where trying to think of the physics by itself and do some handwaving it could easily lead to a plane on treadmill situation. Whereas, if you trusted what the math said it was just there and that was that.

Bill, I’ve PERSONALLY observed snipers in action. They even fired a shot on a range and did NOT compensate for coriolos effect. The bullet was off of the mark enough to NOT make a kill.
Buildings are NOT as precise as sniper solutions.
Think either heart or head at 1.5 miles. A REAL small margin of error. Think that the target is essentially 3.5 inches CEP.
It gets REAL big for that, whereas the building isn’t moving at all. Nor is the bridge moving much, though resonance may become a factor, especially with energy input of wind…

I think billfish678 meant that the coriolis effect is apparent when one does the math, and not ‘fall out’ as in disappears or cancels out. At least, in my introductory physics class the coriolis effect was shown by doing the math.

Also, a mechanics course does not necessarily have anything to do with buildings.

What if the gun was fired from an airplane on a treadmill?

Yes.

This is what I meant. I personally think thats what I actually said as well though others differ in that opinion :slight_smile: