US Police vs. UK Police ???

[UberPhLuBB]

"I say, does my machine-pistol say 'replica' on the side? I seem to be getting funny looks from the passersby, what what."

"It most certainly does, and I hope we are not required to do more than keep these off the ground. I don't suppose they told you how to hold one of these and look intimidating? I feel like a bloody fop."

 

[Control Group]

However per the original from firefighter - I can think of no way that ''g'' can accelerate a downward travelling projectile to achieve anything like original MV - which we might assume to be from a carbine 9mm - something like 1200 and more fps

Hrm

I hadn't thought about it that way, though of course I should have. You're right: once the bullet has reached its maximum altitude, the only things we have to worry about are wind resistance and g. So, using 1200 fps (both because I trust your estimate on speed, and because that's not much past Mach 1, and I know wind resistance dynamics change drastically at Mach 1), for the round to accelerate to that speed due to g, even ignoring drag, it would have to be falling for 37.5 seconds (unless my math is off, of course). This seems like a really long time, to me.

By the same token, if it started out at 1200 fps, it would take 37.5 seconds for gravity to bring it to a halt, too. It won't take that long in atmosphere, of course, because drag will add to gravity's 9.8N (with apologies for mixing SI and English units). On the way back down, then, it won't have to fall as far, which also means it doesn't have as long to accelerate, so you must be right - it can't possibly land with the same velocity it had going up.

And, in a Eureka moment, I just understood why. On the way up, you've got three forces: the initial acceleration (up), wind resistance (down), and gravity (down). On the way down, you've got two forces: wind resistance (up), and gravity (down). Given that gravity's a constant, and assuming that the drag curves roughly match each other, the "down" forces on the way up are higher than the "down" force on the way down.

Rusty, my Aunt Petunia's patootie...you just answered for me a question that's been mildly bothering me for years.

 

[iapetus]

These ones all have their guns pointing down, although they don't look particularly ready for action either...

http://www.timesonline.co.uk/article/0,,22989-1703933,00.html

 

[RyanM]

I forget how to do the actual math, but in the absence of air resistance, a bullet fired straight up will indeed hit the ground at muzzle velocity. So no firing guns upwards on the moon!

With air resistance, terminal velocity is pretty limited. Someone, I can't remember who right now, did an experiment decades ago with M2 ball (.30-06, not .50 BMG) fired straight up. Terminal velocity was 200-ish FPS, and one of the bullets hit a wooden dock on the way down, making a 1/8" deep dent. 200 FPS can still kill you, though. That's probably all the velocity some of those really tiny black powder derringers are capable of, and those've sent many a gambler to an early grave.

 

[Mad Hatter]

The numbers I've got for falling bullets are for a .308 150 gr. flat base: 300 fps, 30 ft-lb. It probably wouldn't do more damage than a bruise and a headache if the person was standing up. But I'm not going to volunteer to stand under one, either. That's gonna HURT.

 

[Eightball]

After reading all of this physics of "if it goes up, will it come down at the same speed?" stuff, my head's beginning to hurt.....

 

[Gunwalker.44]

In the good old days the only Bobbies armed were rare. (#10 Downing St
and places like that). When circumstances warranted they were armed
with whatever surrendered or otherwise available guns they had.
Used to be a great sight, Bobbies in uniform, one with a us military holster
complete with a 1911, next one with a full two gun Western rig and
so on. Yes, they didn't do the 'stop police' stuff, just Bang, gotcha.

 

[entropy]

They're all just slung on a single point, so they of course will be pointing down; these guys look a little more like a reaction force that the preceding pics. The guy in the pic with the gal looks like someone Wackenhut would reject, and they aren't the pickiest.

 

[c-bag]

The UK cops look like decoration, the US cop looks like he's ready to get down and dirty.

True, but on the other hand they do have some downright snazzy hats.

 

[Firethorn]

Firing bullets into the air:

Indeed, in a vacuum, a bullet's down path would be as fast as the up path. However, when you put air resistance into the bargain, it resists movement, period. Thus, the bullet doesn't go up as high, and when it comes down, it stops gaining velocity when it reaches 'terminal velocity', where air friction = gravity acceleration.

From my understanding, bullets can, and have, killed people from being shot into the sky. But it's more along the lines of a simple construction type hard hat would be protection, rather than a full-bore kevlar combat helmet. I'd imagine that larger, longer bullets, having a higher profile density, would have a higher terminal velocity, thus become more dangerous.

 

[Radagast]

Just the other day the Australian press posted a picture of our gun grabbing prime minister on hiatus in London. Out for a photo op jog, his british security detail were standing around in much the same manner. At least the one pointing his MP5 where the PM was about to step had his finger off the trigger. Otherwise there was no awareness of muzzle direction at all. I suppose there would have been some ironic justice if a man who is on record that only the police should have guns was shot by his police bodyguard, but I'm glad it didn't occur.

 

[GunGoBoom]

Firefighter, I must ask whether you are the 'engineer' of your fire dept, meaning that you drive the big red truck to the fire (like a train engineer)? Or maybe a chemical or electrical engineer, because your statement is quite incorrect. The terminal vel of the bullet dropping from the sky will nowhere approach its muzzle velocity - and it's in no way related to the MV - it's related only to terminal velocity if coming more or less straight down, which is determined by wind drag vs. gravity. P95 is exactly correct. It IS, however, still plenty enough to kill someone, if hit in the head or spinal cord, and therefore unwise to intentionally shoot in the air.

However, I must point out a couple of other incorrect or misleading statements by people in this thread. In the event of an ND, having a bullet fired into the concrete jungle of a city from a low ready position (into the ground at an angle) is no less hazardous to bystanders than shooting up into the air at an angle - in fact the danger of ricochet to nearby people is far greater than someone being hit from a falling bullet at a distance.

Second, with respect to the english officer who is holding the pistol grip with his forearm UNDER the buttstock of the rifle - this is not necessarily a deterrent to quick deployment - one can easily lift the end of the buttstock up and over the rear arm and then down into the crotch of the shoulder just as quickly as pulling it up under the arm - neither is as good as having the longarm already shouldered, with a good sling and a low ready, but failing that, what the english cop is doing is no worse than holding the pistol grip over the buttstock. However, the other guy, who is just holding the base of the buttstock - that is silly and would slow him down if something happened.

As for judging one's training by the *look on their faces*? WTH?

 

[carebear]

GGB,

Just guessing but I would think a round impacting concrete at a close to 45 or steeper angle about 3 ft. from the muzzle would be more likely to disintegrate against the concrete or bury itself in the asphalt than to ricochet.

Most ricochets I've seen on concrete were fairly shallow angle impacts.

I think the threat is greater for a round to come down on someone blocks away rather than skip back up from such a steep impact.

 

[UberPhLuBB]

^ Ditto. It might throw some asphalt chunks but it would almost certainly disintegrate.

 

[Riktoven]

I have a sneaking suspicion that most of the bullets that just "fell out of the sky and killed someone" weren't shot straight up. While terminal velocity may be 200 fps, that is only one vector of movement of any non vertical shot. If the shot was fired at 45 degrees, that bullet is going to be moving a lot faster than 200 fps when it comes down (200fps down, X fps in the horizontal vector of travel).


As long as we're discussing physics, anyone know what would REALLY happen if I dropped a penny from the observation deck of the CN tower? Physically to the concrete below I mean, not legally to myself.

 

[Control Group]

As long as we're discussing physics, anyone know what would REALLY happen if I dropped a penny from the observation deck of the CN tower? Physically to the concrete below I mean, not legally to myself.

Nothing notable.

Mythbusters covered this one a while back. They determined maximum velocity of a falling penny (by dropping it down a tube, and increasing airflow from the bottom up until the penny stayed suspended), then constructed a device to fire the penny down at somewhat more than that velocity. By the end, Adam was holding his hand under the gun. Even he admitted, though, that it really stung when the penny hit him in the same spot the second time.

They also rigged up an actual gun to drive the penny downwards at bullet speeds (~1000 fps?), and even that didn't materially damage the concrete. Basically, a penny just doesn't have enough mass to be a good kinetic energy carrier.

For a somewhat more scientific analysis (I love the Mythbusters, but scientists they're not), check out http://www.jimcarson.com/a/000148.shtml

 

[Jim K]

"I forget how to do the actual math, but in the absence of air resistance, a bullet fired straight up will indeed hit the ground at muzzle velocity."

Huh? Sorry, but not true.

When a bullet is fired straight up, it reaches a point in the air at which it stops before starting back down. (Try it with a baseball.) Since it has stopped, it will achieve the same terminal velocity as if it were simply dropped from that point. Since a bullet coming straight down (on Earth) will gain velocity at 32 fps/s in a vacuum, it will reach a terminal velocity based on its time of return. The muzzle velocity of the rifle that fired it is a factor only in that the more powerful the rifle the farther up the bullet will go, so its downward time of drop will increase, increasing its terminal velocity slightly. But it would never come anywhere near muzzle velocity.

Jim

 

[odysseus]

The numbers I've got for falling bullets are for a .308 150 gr. flat base: 300 fps, 30 ft-lb. It probably wouldn't do more damage than a bruise and a headache if the person was standing up. But I'm not going to volunteer to stand under one, either.

Thing is, it's parabolic. I think your example is about dropping a round from like the empire state building or something. So it depends on the angle and attitude when fired. It is going to retain a lot of energy normally, since it is not going to loose all of it's energy to friction and gravity. That's how some people can die from a ND into the air, which is mostly the situation if that round finds a person as a landing.

 

[Control Group]

When a bullet is fired straight up, it reaches a point in the air at which it stops before starting back down. (Try it with a baseball.) Since it has stopped, it will achieve the same terminal velocity as if it were simply dropped from that point. Since a bullet coming straight down (on Earth) will gain velocity at 32 fps/s in a vacuum, it will reach a terminal velocity based on its time of return. The muzzle velocity of the rifle that fired it is a factor only in that the more powerful the rifle the farther up the bullet will go, so its downward time of drop will increase, increasing its terminal velocity slightly. But it would never come anywhere near muzzle velocity.

Sorry, this is wrong. And it's easily demonstrated. Absent air resistance, it will reach the ground (actually, it will reach the altitude at which it left the muzzle) at exactly its muzzle velocity. Consider:

Assume the bullet leaves the muzzle at 3200 fps, straight up. Gravity accelerates it down at 32 feet per second per second. That means it will take 100 seconds to reach zero velocity (relative to the planet, that is). Since we're dealing with constant acceleration, it's easy to figure average velocity, it's the average of initial velocity and final velocity, so 1600 fps. 1600 fps over 100 seconds is 160,000 feet.

Now, if you're right, and the bullet never reaches 3200 fps again, it should take longer than 100 seconds for it to return (since, starting from zero, it has to reach 3200 fps to average 1600 fps, which will cover 160,000 feet in 100 seconds). So it will be accelerating due to gravity for at least 100 seconds.

Of course, 100 seconds of accelerating at 32fps/s will give it a final velocity of 3200 fps.

 

[P95Carry]

Riktoven - welcome

anyone know what would REALLY happen if I dropped a penny from the observation deck of the CN tower?

Yep - it'll be a head or a tail!

 

[jaysouth]

Can't speak to doctrine for police in U.K., but the British Army has been carrying muzzle down with the butt toughing the strong shoulder since their first auto loading (FAL/SLR) weapons were issued in the late 50s.