Monday, January 22, 2018

Physics! The Coriolis Effect

Instapundit says, I'm a pretty good shot for a law professor. But this is the biggest of the big leagues: The world's longest sniper kill: The enemy shot dead at 3,871 yards (over 2 miles away)

The professor's regular confident self-affirmation is charming.

The link goes to National Interest, The Buzz.
To understand the complexity of the shot, it’s best to start with a sniper maxim: sniping is weaponized math. Although a .50 caliber sniper rifle bullet can fly as far as five miles, a host of factors including gravity, wind speed and direction, altitude, barometric pressure, humidity and even the Coriolis Effect act upon the bullet as it travels. 
Okay, wait a minute. I heard of that before. What is it again? The Coriolis Effect. The bullet spins and turns it into a gyroscope. Right? But instead of keeping it steady and balanced, the spin pulls the forward motion to the side. Right?



The whole story is interesting, and a bit frightening, but this bit seemed particularly so. Imagine being a sniper and needing to account for this, to intuit it. If you asked the sniper directly (Canadian), he'd go, "Lucky shot." And seeing how this basketball moves with so little spin you can see how that would take a lot of practice.

4 comments:

Chip Ahoy said...

This video is an edited version of a longer video by the same team (narrated by an American without the Australian speech impediment) where the spin is called the "the Magnus Effect" while stating that Isaac Newton described the same thing previously. The diagram is interesting. It shows the air being pulled around the ball by the spin and running into the wall of air on the opposite side, and that's what forces the ball to move in the direction opposite its spin. Then the video shows how this is used on airplanes (fail) and on boats (win).

The Dude said...

Guy I used to work with was a gunny - he fired artillery rounds long distances. He told me they had to compensate for how far a target would travel due to the earth's rotation while the round was in the air. He also discussed how the wind would affect the accuracy of even a large caliber round moving at supersonic speed.

Fascinating stuff. Much maths.

rhhardin said...

Coriolis is an effect of a rotating coordinate system, which you tend to adopt if on a rotating earth. The objects move straight, as you'd expect, but you don't expect your coordinate system to move since you never notice it otherwise.

Spin (aka curveball) has to do with air motion. The back of the ball has the last say and throws air with it in the direction it's spinning. The reaction curves the trajectory.

Bullets have only the coriolis problem. You have to shoot where the guy is going to be when the bullet gets there, taking into account that the earth you and he are on is rotating.

The Dude said...

Why did the basketball that was dropped with no spin move to the right in the video? What force was acting on it to make that happen? Guy never delves into that. Incurious, I guess.