A friend proposed the theory that if one fires a gun directly into the air (relatively perpendicular to the ground) that due to the earth’s rotation (adjusted for our latitute in the SF Bay Area)& the time it takes the bullet to reach it’s apex and then descend that the bullet would land roughly 80 miles from where it was shot.
I think he’s yanking my chain - the atmosphere must affect it somehow. But, obviously I missed out on Physics 100. Can somebody enlighten me? TIA.
I couldn’t tell you the scientific principles behind it, but I think the bullet would be affected by the momentum of the spinning Earth and gravity. In other words, even though it’s been shot into the air, it sort of gets dragged along with us as the Earth spins. Thus, while I doubt it would land on your head, it probably would end up a lot closer than 80 miles from you.
Soup is right … it would land somewhere away from you, but not nearly 80 miles away. The earth’s rotation (Coreolis effect - I bet I spelled that wrong) will change the bullet’s landing point somewhat even in the absence of wind, but not too much. The bullet will land slightly to the West of you, more if the muzzle velocity is high, less if it’s less.
The bullet is being shot from a gun that’s moving at the same speed as the earth. That speed is transfered to the bullet. It’s all relative.
Your friend is the kind of idiot who shoots himself (or worse an innocent passerby) by shooting into the air on New Year’s Eve. You’ll see dozens of such incidents reported in the news on Saturday.
I don’t think this is true. Barring wind and irregularities in the gun or bullet, a projectile propelled straight up will land precisely where it was fired. You’d have to fire the bullet into orbit before the Earth’s rotation would have an effect. Any artillery vets out there?
I don’t think so, Ursa.
The horizontal momentum is in the direction to the earth’s rotation, but friction from the air resistance will slow that momentum. Therefore, it wouldn’t land where it started but only by the amount of horizonal air resistance.
One of these math people can figure out how soon the bullet will return to earth, but it shouldn’t be very far away.
But surely the air is also moving at the same speed as the Earth. There would be no horizonal air resistance.
Am I missing something?
Hmmm, maybe not, Ursa. I bow to you on this.
If there were a god, the bullet would come right back to the shooter. Maybe just in the foot or something.
I’ve never understood the attraction of this idiotic behavior. And it’s almost exclusively a male thing. How embarrassing.
Peace,
mangeorge
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Love like you’ve never been hurt…
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P.J. O’Rourke said in his book Give War a Chance that several people were killed the night that Kuwait City was liberated by bullets fired into the air that came down on people’s heads. I doubt that any of the people killed were actually those who fired the bullets. Still, if P.J. is not
B.S.ing, there’s some concrete evidence that that theory is wrong.
As for theoretical evidence, how long does it take for a bullet fired into the air to hit the ground? I dunno, let the physics jocks figure that one out, but a couple of seconds at most. Not enough for the Earth’s rotation to make any difference, and certainly not eighty miles’ worth. Or for the atmosphere to make a difference.
Yes, it would come down more-or-less from where it came up, if there’s no extremely strong winds.
“If first you don’t succeed, try, try again…then quit, there’s no use in being a damn fool about it.” - W. C. Fields
DON’T go shooting guns off straight in the air or even angled in the air. I have read of some instances where the bullet has come back down, virtually as fast as it went UP and KA-BLANGED the shooter with nasty results.
I worked in a place one New Year’s Eve, on the edge of a high crime district and at midnight it sounded like WW2 started up. We had to pull everyone away from outside windows because of the potential not only of stray shots, but snipers and spent bullets thudded down on the roof!
Most people know – though there are some who DON’T – that a bullet shot into the air has to come down somewhere, with the same force as it left with. If it strikes a person, it can do the same amount of damage that it would if the shooter were right there. I worked at a warehouse miles away from a high crime area and would often find spent bullets on the ground, and a corresponding chip taken out of the concrete wall of the building.
By the way, unless you have a high powered rifle, your bullet is NOT going to go that high into the air. Gravity is going to affect it real fast. Examples of this can be seen at a shooting range where they use tracers to mark their bullets flights. I was quite stunned to see just how a high powered rifle’s slug is affected so soon by gravity. A .22 slug states that it will travel a mile, BUT you have to make adjustments in elevation to get it to do so or else it will hit the ground in about 50 yards or less.
Now, consider shooting it straight up with gravity affecting the vertical climb, which means it will start becoming affected by drag instantly. That’s why the shuttle doesn’t go straight up but takes off at a steep angle.
High School Physics:
Assuming no wind, air resistance, blah blah, as an object passes point X going up, it will have the same speed at point X coming down. Meaning when the bullet lands, it’s going just as fast as it was shot.
Don’t prove it.
JMcC, San Francisco, JJM’s page from the Bay
If I were beaned with a fastball, fling my limp, lifeless body to first, cause, dammit, I earned it!
Wow. Lots of misconceptions here.
First, all things are not relative. Acceleration, for instance. As in a turning Earth. That’s what the Coriolis force is all about, and it should cause the bullet to fall some distance to the west of you, but I don’t think the effect would be that significant. 80 miles is ridiculous, since a bullet fired from a gun will rarely travel more than a mile or two from the shooter in the first place.
Second, a falling bullet will NOT land at ‘almost the same speed it went up’. Not even close. High-powered rifle cartridges fire bullets at supersonic speeds, and the terminal velocity of a streamlined bullet is probably in the neighborhood of 100-200 mph. If that. It could be a lot less, since bullets are not very massive and their small size makes them more susceptible to atmospheric drag.
Finally, there is no way in hell a .22 bullet will drop 6 feet in 50 yards. I believe the drop at 50 yards would be more like a couple of inches.
Cecil has addressed this question: http://www.straightdope.com/columns/950414.html
The coriolis force is probably not as significant as small deviations from the vertical when trying to shoot straight up.
For a just-subsonic .22, it would take about a seventh of a second to go 50 yards, which is a drop of 1/2 * 1/7 * 1/7 * 32 * 12 or about 4 inches, plus a bit for the real world.
My impression is that the bullet would land to the east of where it was shot from. My thinking is that the bullet’s horizontal velocity would remain constant with the earth’s; however, the radius of it’s path would increase meaning that it traveled fewer degrees latitude as the earth so the bullet would land to the east.
You know, doing what is right is easy. The problem is knowing what is right.
–Lyndon B. Johnson
Physics is wonderful, and you folks can hypothesize 'till the cows come home, but there is no subtitute for real experimentation. When I was young and stupid (as opposed to my current older and stupid state), we really wanted to know what would happen to a projectile fired straight up from a gun. The laboratory was the woods behind our house (the better to hear the projectiles returning to earth through the trees, leaves, etc). The tests were coducted with a shotgun loaded with bird shot (again, to have a better chance of hearing the shot fall). The experiment - fire the shotgun straight up, head for cover, listen for the results - was repeated several times. In every case, a few seconds after firing, we heard the bird shot fall like rain through the trees and underbrush around us.
Not exactly a double-blind study, but pretty conclusive.
The overwhelming majority of people have more than the average (mean) number of legs. – E. Grebenik
I thought this was one of the first things they taught, too. I saw them do it in an educational film & it comes straight down theoretically but winds,etc as with the bird shot, makes things scatter a bit.
Don’t do it in SF. There are too many people.
You could easily calculate the velocity of the bullets when they hit ground.
Not ‘easily’. The velocity of the bullet when it hits the ground will almost certainly be its terminal velocity. What that terminal velocity is depends on the mass of the bullet, its cross-sectional area, shape, and whether it is tumbling or not. It would not be a simple thing to calculate, and every calibre of bullet will be different.
Maybe it would help if I explaine the Coreolis effect better. How fast the earth turns is constant in angle at any altitude or depth (at a given latitude). In velocity (i.e. in feet per second) it varies with altitude. Someone on top of a mountain is moved faster by the earth’s rotation than someone in a valley. A chunk of core rock (at the same latitude) is moving very slowly, since it travels in only a small circle every day.
Someone on the edge of a merry-go-round must hold on more tightly than someone in the middle.
When you fire a bullet straight up from sea level, it has X amount of eastward velocity imparted to it by the Earth’s rotation. It immediately ascends to altitudes which would require X + Y velocity to stay above the same point, but it never gets that velocity. Instead, it lags behind the Earth, ending up at a position somewhere to its West.
Another way to illustrate this would be, imagine you have a gun at the very center of the earth, which fires a projectile with ordinary mass but it somehow can penetrate like it was vaccuum. Okay, you have to have a really good imagination for that one, but bear with me. So this gun fires in any direction (except directly toward either pole). Let’s say it fires at Maryland. Where will Maryland be by the time the projectile gets there? Somewhere to the East. If the bullet is slow enough, it’ll land in Missouri, or Japan for that matter.
Yes, this effect is likely to be tiny with a low-velocity projectile, especially relative to wind conditions and inaccuracies in vertical aim. I’m merely explaining the theory which I think the OP was alluding to.
In any case, firing a gun in any direction other than at an approved backstop is a bad idea. You’re not likely to shoot yourself, nor are you likely to shoot any single person in particular, but in a city there are going to be hundreds of people in the radius of a few hundred meters, so you could endanger the health and lives of any of them. Property damage is another concern. The bullet will fall at terminal velocity, which isn’t high relative to muzzle velocity, but it’s still a narrow chunk of heavy metal which could easily crack someone’s skull. I sincerely hope that no one is injured tonight, and if they are, I hope the perpetrators get put away for a nice long time.