Got a Real World Weapons or Armour Question? Mk X

[Yukitsu]

According to those NIJ standards, 7500 J is energy at which type IV (armor piercing rifle) vests will generally start to fail quite often.

Those are powerful loads, obviously from long barrels.

They have theirs in the proper Ek calculations though, whereas I'm lazy and just using the SI unit. 7500 at the SI unit is an Ek of 3750 Joules.

[Autolykos]

[RANT]
WTF? A Joule is a Joule is a Joule. There is only one kinetic energy, and that doesn't depend on whether you use SI, Imperial, CGS, or some other weird unit system.
The correct way to calculate it is E=1/2 m*v², and nothing else (unless you insist on correcting for special relativity...). Using another formula (like m*v²) is just plain wrong. Whatever you're calculating there, it's not the kinetic energy of the projectile, and shouldn't be called that.
[/RANT]

Sorry, but that just had to be said. My earlier point was more about the implausible precision (7 significant digits when even the second one was probably already inaccurate). I didn't mean to pick on you, but stuff like that really gets my goat.

[Yukitsu]

Ek is calculated as 1/2 mv^2 (1/2md^2/t^2), and is referred to in Joules (the SI unit), where 1/2 is a constant that doesn't have anything to do with joules, but is related to Ek.

A Joule as an SI unit of measurement is mxd^2/t^2.

I'd have to double check why, but I'd have to dig up my old text books.

Number is "precise" because putting through a number with a possibly inaccurate decimal in the kg portion of the equation didn't get a perfect number.

Either way though, Ek is expressed in Joules, but you don't get to say that the calculation for Ek is identical to the derivation for Joules.

http://www.physicsclassroom.com/class/energy/u5l1c.cfm

[Conners]

With all the crazy inventions we have nowadays... what would a proper war be like? Stuff like the Javelin seems to make Armour (tanks and vehicles) completely useless, since an infantryman can take out about as many tanks as they have javelin rockets. Artillery can also shoot incredibly precisely at incredibly long ranges, now... and you get all those stealth drones which drop more drones, all of which have killing capabilities.


Any ideas what a full-out war would be like nowadays? If it were America against a non-super power, I can see it being more of a slaughter rather than a war. But I have trouble fathoming what a war between two super powers would be like nowadays.

[Tarinaky]

With all the crazy inventions we have nowadays... what would a proper war be like? Stuff like the Javelin seems to make Armour (tanks and vehicles) completely useless, since an infantryman can take out about as many tanks as they have javelin rockets. Artillery can also shoot incredibly precisely at incredibly long ranges, now... and you get all those stealth drones which drop more drones, all of which have killing capabilities.


Any ideas what a full-out war would be like nowadays? If it were America against a non-super power, I can see it being more of a slaughter rather than a war. But I have trouble fathoming what a war between two super powers would be like nowadays.

The trouble with things like the Javelin is there are anti-missile-missiles that will pick up a laser designator and fire first.

[Autolykos]

Either way though, Ek is expressed in Joules, but you don't get to say that the calculation for Ek is identical to the derivation for Joules.
http://www.physicsclassroom.com/class/energy/u5l1c.cfm

No. These are to different things. Kinetic energy is a physical quantity, Joule is a unit of measurement. You can express a specific quantity in different units of measurement (kinetic energy can be expressed in Joules, Erg, or whatever strange unit the Americans use), but saying "I calculated Joules, not kinetic energy" just doesn't make any sense.

[Yora]

There was a question in the Friendly Banter forum, which I copy here since you guys might have some answers:

In short, I discovered my grandfather owns a shotgun. But not any kind of shotgun; apparently it's a family heirloom he inherited from his father. As to know whether his own father inherited it from his own father is up to speculation. So we know the weapon is pretty old.

Being the sole direct male heir of this branch of the family, I know I will be entrusted the weapon in the future. I wanted to know what sort of gun it is. For what they've told me, it's a shotgun of Germany origins, capable of shooting 6 shots. But for what my grandparents told me, the 6 shots aren't loaded in a barrel (the way a revolver would).

From that alone, anyone have any idea what this gun's brand might be?.

[eulmanis12]

There was a question in the Friendly Banter forum, which I copy here since you guys might have some answers:

so we know that the gun fits this description.
Very Old, at least 1800's
German
Multi-shot
a shotgun
not a revolver
not magazine fed

Not much detail to go on, but I can think of some firearms that might fit the bill.
There were numerous specialty guns manufactured in the late 1700's up through the mid 1800's that fired multiple charges by "stacking" the rounds, ie. lining them up one after the other inside the barrel. Most of those didn't have a specific "type", instead they were one offs made for a specific client by a gunsmith that was pretty much just showing off.

more detail, and if possible a picture would be helpfull. The above is just a theory and is probably incorrect.

[Triscuitable]

so we know that the gun fits this description.
Very Old, at least 1800's
German
Multi-shot
a shotgun
not a revolver
not magazine fed

Not much detail to go on, but I can think of some firearms that might fit the bill.
There were numerous specialty guns manufactured in the late 1700's up through the mid 1800's that fired multiple charges by "stacking" the rounds, ie. lining them up one after the other inside the barrel. Most of those didn't have a specific "type", instead they were one offs made for a specific client by a gunsmith that was pretty much just showing off.

more detail, and if possible a picture would be helpfull. The above is just a theory and is probably incorrect.

When he says "very old", he meant his grandfather owned it. That means going back roughly 80 years. If his great-grandfather owned it, go back another 40. That's the late 1800's that he would've been born in, so it's safe to assume the gun is an 1887 or 1900's manufactured shotgun. If it was pump, then it's almost definitely an 1887. Of course, that last sentence is just a guess, but hey, we have almost nothing to go by.

[fusilier]

When he says "very old", he meant his grandfather owned it. That means going back roughly 80 years. If his great-grandfather owned it, go back another 40. That's the late 1800's that he would've been born in, so it's safe to assume the gun is an 1887 or 1900's manufactured shotgun. If it was pump, then it's almost definitely an 1887. Of course, that last sentence is just a guess, but hey, we have almost nothing to go by.

I would guess it's some sort of pump action as well, based upon the original post. Note, that he didn't say it lacked a magazine, just that it wasn't loaded like a revolver.

Super-imposed loads are dangerous things, and six would be a lot of them! Unless it was designed to fire all six in immediate succession, it would require too many locks to be wieldy. If it was designed to fire all six loads immediately, then it would probably only have utility as a military weapon.

[huttj509]

No. These are to different things. Kinetic energy is a physical quantity, Joule is a unit of measurement. You can express a specific quantity in different units of measurement (kinetic energy can be expressed in Joules, Erg, or whatever strange unit the Americans use), but saying "I calculated Joules, not kinetic energy" just doesn't make any sense.

Indeed, it's like saying "I calculated the meters of the bus, not the length." "The meters" could refer to length, width, height, diagonal, etc. It's not a physical attribute of the bus. "The Joules" could refer to kinetic energy, potential energy, rotational energy, temperature (yes, temperature can be measured in units of energy, threw me when I heard people measuring temperature in eV).

One Joule is one kilogram*meter/second^2. That is the unit. It's like saying 1 foot is 12 inches. If you calculate 1/2 mv^2 with m in pounds(mass), and v in furlongs per fortnight, you don't get an answer in Joules, you need to convert the Furlongs to meters, fortnights to seconds, and pounds (mass) to kilograms.

[Conners]

How quickly do war horses tire, generally? Do you need to change horses once every hour, or ten minutes?

[Autolykos]

How quickly do war horses tire, generally? Do you need to change horses once every hour, or ten minutes?

I don't know about warhorses specifically, but in general, horses tire slightly faster than humans. The Romans didn't like cavalry very much because they found it reduced their strategic mobility. Training and breeding can make a lot of difference, though. The Mongols were a lot more mobile on the strategic level than most infantry-heavy armies of the time.
If you're talking about the late-medieval warhorses with heavy armor and an armored knight on top, I just don't know. They were probably bred for strength (and stupidity) rather than endurance, so they'd tire a lot faster than Mongol horses (or even the average saddle horse).

[Galloglaich]

The Mongols were mobile because they brought as many as 6 horses per rider with them on raids and war deployments.

Knights also brought many horses with them on campaign and generally didn't travel on their warhorses, they would travel on a horse like an ambler which was for walking in the (easy on the rider and horse) ambling gait, or a courser which also knew that gait but could run if necessary.

When they went into battle they would mount their charger (destrier or palfrey, or a courser).

A typical heavy cavalryman in the late Medieval period would have at least 3 horses, plus another horse or a mule as a pack animal, plus horses for their armed attendants of which they would normally have 2-5 with them.

G

[Joran]

With all the crazy inventions we have nowadays... what would a proper war be like? Stuff like the Javelin seems to make Armour (tanks and vehicles) completely useless, since an infantryman can take out about as many tanks as they have javelin rockets. Artillery can also shoot incredibly precisely at incredibly long ranges, now... and you get all those stealth drones which drop more drones, all of which have killing capabilities.


Any ideas what a full-out war would be like nowadays? If it were America against a non-super power, I can see it being more of a slaughter rather than a war. But I have trouble fathoming what a war between two super powers would be like nowadays.

I think everyone is having trouble fathoming what a war between super powers would look like. The last great war was World War 2 and since then there have been a couple of proxy wars (U.S. in Vietnam, Soviet Union in Afghanistan), but no real head to head conflict between equally matched opponents. Technology has rapidly advanced.

Well, actually, "full-out war" is pretty easy to imagine: ICBMs on every major city. Assuming a conventional war, it's going to really hinge on what the objectives are, where it's fought. A war between the U.S. and China over Taiwan is going to be mostly fought in the air and in the water. A war with Russia and Europe is going to be fought mostly on the ground and in the air.

Wherever the war is fought, air superiority is pretty much key. I don't think we've had advanced fighters like the F-22 (when it's not suffocating the pilots) against the best of the best either, so that's a major question mark.

The battle over electronics might get ugly, with counter-attacks via the Internet on civilian and military infrastructure and especially nasty if one side decided to shoot down satellites.

To sum it, I don't think anyone really knows how the next great war will be fought and which counter-measures will work and how all these advanced weapons will affect it. A lot of the specifics will be based on where the war is fought and for what objectives. I for one hope I never see it in my lifetime.

[Galloglaich]

me either.

The other big factor besides the ones you mentioned: robots.

G

[Joran]

me either.

The other big factor besides the ones you mentioned: robots.

G

Very true, autonomous robots. Drones piloted by humans may play a key role, or they may be obsoleted quickly because the enemy attacked the communications infrastructure =P

[fusilier]

How quickly do war horses tire, generally? Do you need to change horses once every hour, or ten minutes?

It depends upon what the horse is doing. Ideally you want to keep your horse "fresh" for that perfect moment to charge, which would entail a sudden burst of speed but be over fairly quickly. How much equipment the mounted soldier is carrying on himself and the horse will also be a factor. A knight would often have several horses on campaign, although I suspect only one would be the preferred battle horse, the others primarily intended for riding long distance. The Spanish presidial troopers in Northern Mexico took 5 to 6 horses with them on campaign -- a lamentable practice because the dust kicked up announced their presence well in advance, and the herds were too large to effectively guard. 19th century American cavalry, each man having only one horse, would spend one hour riding and the next hour marching next to their horses.

[Yukitsu]

No. These are to different things. Kinetic energy is a physical quantity, Joule is a unit of measurement. You can express a specific quantity in different units of measurement (kinetic energy can be expressed in Joules, Erg, or whatever strange unit the Americans use), but saying "I calculated Joules, not kinetic energy" just doesn't make any sense.

You can say it all you want, but a Joule is J=m*d^2/t^2, while Ek=1/2m*d^2/t^2 and is in Joules. I honestly just used the former when I shouldn't have, as while I know offhand what a Joule is, I didn't remember the constant for Ek.

It's pretty much exactly like how surface area is in m^2, but the surface area calculation for a right angle triangle is ab/2, but is still referred to in the unit metres squared. If you just did ab, you'd end up with metres squared, but you're doing it for a square, not a triangle.

[Autolykos]

a Joule is J=m*d^2/t^2

Now there's your problem. Joule is kg*m²/s², and a unit (just like kilogram, meter and second are). Kinetic energy is a quantity, and 1/2*m*v² (just like mass and velocity are quantities). Having quantities on one side of the equation, and units on the other doesn't make any sense. The formula you found describes the unit "Joule", and says *nothing* about any quantities expressed in the unit.
The confusion might stem from you misreading the second equation in your source. It says: One Joule is one kilogram multiplied by one meter squared, divided by one second squared. No more, no less. In particular, it doesn't say *anything* about any energies, masses or velocities. That's in the first equation.

surface area is in m^2

Here, you actually did it right. Saying "surface area is m^2" doesn't make any sense. Surface area is a quantity, m^2 is a unit. The correct way to put it is "surface area is in m^2", like you (instinctively?) did here.

But I'm beginning to think that if you neither understand (or care to read) the Wiki articles I linked to, nor the very good explanation by huttj509, there isn't much hope left to explain you the difference. As it's starting to become quite off-topic (even though physics will regularly come up in this thread), I'll leave it at that.

EDIT: Probably the best I can do is give you a practical guide: If you want to calculate quantities (like kinetic energy), look for a formula containing quantities. If you want to convert units (like meters per second to miles per hour), look for a formula containing units. Mixing those up gives meaningless results and makes physicists very sad.

[Yukitsu]

Here, you actually did it right. Saying "surface area is m^2" doesn't make any sense. Surface area is a quantity, m^2 is a unit. The correct way to put it is "surface area is in m^2", like you (instinctively?) did here.

I do it the same way with Ek. Ek is in Joules.

But I'm beginning to think that if you neither understand (or care to read) the Wiki articles I linked to, nor the very good explanation by huttj509, there isn't much hope left to explain you the difference. As it's starting to become quite off-topic (even though physics will regularly come up in this thread), I'll leave it at that.

I'm not sure why I would care about those wiki articles I (and if I do look it up, I'll use a text book), as I've already mentioned I used the unit measurement when I should have used the Ek calculation. You're the one who jumped down my throat because apparently, you think they should have identical values or something, I don't know. The only difference in any event, is a constant that I noted after the fact.

[fusilier]

I do it the same way with Ek. Ek is in Joules.

I'm a bit confused by all this, and rather hesitant to get involved, but I just want to make sure we are all clear on one thing:

Kinetic Energy (Ek), doesn't have to be expressed in joules. In the US it's common to use foot-pounds -- which is also a measurement of torque (turns out that torque and energy have the same dimensions, and 1 joule = 1 Newton-meter).

There are many many units of measurement we could use to measure kinetic energy, although some tend to be used only in special circumstances/conditions. Nevertheless, we could talk about kinetic energy in terms of watt-hours, BTUs, and electron volts. Although it would be pretty silly: How many calories did that bullet have when it contacted the armor plate?

[Autolykos]

@Fusilier: That's completely correct (except for the tiny bit with energy and torque, which I'll explain later). 3750 J = 895 cal, by the way. Or roughly 20 sextillion electron Volts.
It's just not the point I was fighting over. Maybe I explained it badly (English is not my native language). The important point was that you can't insert quantities (like the mass of a projectile, or a specific value like 50 grams) in a formula containing only units (like his 1J=1kg*m²/s²), since there are no quantities in that formula to replace. The reason I was getting so upset about it is that this misconception is quite common among pupils and a huge hindrance in understanding physics. I didn't want to let that go uncommented.

As to energy and torque using the "same" units, explaining that requires some math. I try to put it as simple as possible, but feel free to ask (or look it up on Wikipedia) if I'm unclear. Also, the limited set of characters in this forum might make the formulas hard to read.
Force and distance are both represented by vectors. That means they have a value and a direction. There are two ways to multiply vectors, commonly called "dot product" and "cross product". If a is the angle between the vectors, the dot product of the vectors v and w (with non-bold v and w being their length) is:
v.w=v*w*cos(a)
which is a scalar (it doesn't have a direction). The cross product (z=vxw) has the length
z=v*w*sin(a)
and is perpendicular to v and w. Especially, it's still a vector.
Now, energy is the dot product of force and distance, while torque is the cross product. So the units *should* be written as N.m and Nxm, but this is commonly left out, and both are read as "Newtonmeters", which can be the source of some confusion.

[Brother Oni]

Very true, autonomous robots. Drones piloted by humans may play a key role, or they may be obsoleted quickly because the enemy attacked the communications infrastructure =P

Not neccesarily - I know some work on autonomous drones are being done, so they can idle/patrol but still detect threats while the operator can catch a quick breather.

The next step I've heard, is giving these drones independent authorisation to engage targets, so all you need to do is send up a bunch of drones to patrol this area and they'll automatically destroy any targets that enter, making it a potentially effective area denial system.
Knocking out the comms won't have an effect since they're pre-programmed to patrol this area for x hours then automatically return to base.

There's also the automated sentry guns that I've seen prototypes on youtube for. I'm not sure how effective they are, but the fact that somebody's built a prototype indicates that somebody thinks there's potential in the idea.

[Dead_Jester]

The next step I've heard, is giving these drones independent authorisation to engage targets, so all you need to do is send up a bunch of drones to patrol this area and they'll automatically destroy any targets that enter, making it a potentially effective area denial system.
Knocking out the comms won't have an effect since they're pre-programmed to patrol this area for x hours then automatically return to base.

And there is no way that can go wrong... Any glitch in the video system, or in the identification system, and you have a major political incident on your hands. Plus, you'd have to account for variable rules of engagement on the fly, including from the presence of innocent civilians and/or hostages, and the possibility of your enemies surrendering.

I do think that we will see in increase in robotics in military fields, but mostly in indirect roles (piloting, target acquisition, reconnaissance); letting a robot find a target is one thing, letting it pull the trigger is another one entirely.

[Tarinaky]

Not neccesarily - I know some work on autonomous drones are being done, so they can idle/patrol but still detect threats while the operator can catch a quick breather.

The next step I've heard, is giving these drones independent authorisation to engage targets, so all you need to do is send up a bunch of drones to patrol this area and they'll automatically destroy any targets that enter, making it a potentially effective area denial system.
Knocking out the comms won't have an effect since they're pre-programmed to patrol this area for x hours then automatically return to base.

There's also the automated sentry guns that I've seen prototypes on youtube for. I'm not sure how effective they are, but the fact that somebody's built a prototype indicates that somebody thinks there's potential in the idea.

The really interesting thing with drones is the Information Security. I've heard tales that the video feeds from predator drones are unencrypted, or encrypted weakly and there's some speculation among left-wing news outlets that they may even have been intercepted during operations by the enemy.

It's certainly an interesting avenue for speculative fiction regardless of whether real-world examples exist presently.

[Autolykos]

I've heard tales that the video feeds from predator drones are unencrypted, or encrypted weakly and there's some speculation among left-wing news outlets that they may even have been intercepted during operations by the enemy.

That's not rumors, that's a pretty well-known fact. Basically, the operators find it more important that their own guys have access to the video feed at all times without the need to exchange codes (which can, and will go wrong in something as chaotic as a war) than denying enemies that access (they don't profit that much anyway, since they can't choose where the drone is looking). A simple analog feed will also make the construction more reliable, less expensive and easier to repair and maintain.
The commands sent to the drone are properly encrypted, of course. Here, distributing access to people in other units is pretty much a non-issue and the damage an enemy could cause is much bigger.

As for the general question, I don't think a drone should be allowed to decide what to shoot and what not. The systems are not reliable enough, and a human should still have the last word (except maybe for areas where humans have absolutely no business going, like in the border strip between South- and North Korea). Flagging stuff on screen as probable friends/enemies, yes. Pulling the trigger, no. Guiding the projectile/assisting aim, yes.

[Brother Oni]

I do think that we will see in increase in robotics in military fields, but mostly in indirect roles (piloting, target acquisition, reconnaissance); letting a robot find a target is one thing, letting it pull the trigger is another one entirely.

Oh, I fully agree that letting target acquisition software made by the lowest bidder, choose what it shoots is a terrible idea, but that's the rumours I've heard.

Hopefully somebody with sense (ha!) will knock this aspect of the project on the head.

[Tyndmyr]

And there is no way that can go wrong... Any glitch in the video system, or in the identification system, and you have a major political incident on your hands. Plus, you'd have to account for variable rules of engagement on the fly, including from the presence of innocent civilians and/or hostages, and the possibility of your enemies surrendering.

I do think that we will see in increase in robotics in military fields, but mostly in indirect roles (piloting, target acquisition, reconnaissance); letting a robot find a target is one thing, letting it pull the trigger is another one entirely.

Same, same for people. And people aren't 100% failsafe either. If you can get the drones good enough, that's still a win.

Oh, I fully agree that letting target acquisition software made by the lowest bidder, choose what it shoots is a terrible idea, but that's the rumours I've heard.

Hopefully somebody with sense (ha!) will knock this aspect of the project on the head.

Cost is only one factor on military acquisition contracts. There is no guarantee that the lowest cost bidder will in fact be chosen.

[Joran]

Oh, so new to me, maybe not new to you.

There's a website called the Internet Movie Firearms Database, which catalogues every firearm used in movies and TV shows. So, if you've ever wondered "Hey, what weapon was that I just saw?", you can look it up.

http://www.imfdb.org/wiki/Main_Page