For Questions That Don't Merit Their Own Thread

[JoeSchmuckatelli]

9 hours ago, kerbiloid said:

The armored concrete was suggested by the (clay pots for palms) manufacturer who was strengthening the clay with wooden twigs.
XIX century or so.

The twig-armored clay pots are known and widely used since the stone age. It's not necessary to burn them, usually they just dry it under sun.
It's how the pottery appeared at all, since they started to cover twig baskets with clay.

As you have been to Afghanistan, an adobe should also be familiar for you.

I forgot about un-kilned, sun/fire dried for storage.  And yes, we did use stuff like that in the very early days. When you were talking about pots, my focus was on cookware / dinnerware - and non kilned clay does not do well or last long in that arena.  Seeing as pottery was a global human tech very early on, most crockery found is kilned (but then the other stuff would not have survived, would it?). 

But kilned clay was so easy to do and provides so many benefits - that it became globally ubiquitous very early on. 

Adobe is another interesting thing.  I've seen old Adobe structures in Africa, the American Southwest, Spain and the Middle East. Anywhere hot enough and dry enough can let us build some really long lasting structures (as long as they're maintained) with natural fiber reinforced clay.  

 

You gotta really appreciate human ingenuity - someone once looked at, then played with, grass, mud and poop and said 'Look what I can do!' 

And it caught on

[kerbiloid]

8 minutes ago, JoeSchmuckatelli said:

Adobe is another interesting thing.  I've seen old Adobe structures in Africa, the American Southwest, Spain and the Middle East. Anywhere hot enough and dry enough can let us build some really long lasting structures (as long as they're maintained) with natural fiber reinforced clay.  

My grannies owned an adobe house in southern Russia where it's not anywhere as hot as to the south from it, and it happily keeps standing now.

Edited October 26, 2020 by kerbiloid

[JoeSchmuckatelli]

1 hour ago, kerbiloid said:

My grannies owned an adobe house in southern Russia where it's not anywhere as hot as to the south from it, and it happily keeps standing now.

I'm guessing this is in a "Plains" region?  From what I can tell, adobe, mud brick and daub structures are wholly viable in places where there is insufficient rainfall for temperate deciduous or tropical rainforests.

https://www.nature.com/scitable/knowledge/library/terrestrial-biomes-13236757/   Deserts, savanna, Mediterranean and grasslands all have the temperature and intermittent rainfall rates to allow them to survive.  The oldest structures I've visited are in the driest areas.  IIRC, daub structures in England required constant upkeep or they'd disappear in a season, but were very effective at penning and keeping wind out, whereas in the Middle East and North Africa I've seen structures dating from before the Romans.

[kerbiloid]

2 minutes ago, JoeSchmuckatelli said:

I'm guessing this is in a "Plains" region?  From what I can tell, adobe, mud brick and daub structures are wholly viable in places where there is insufficient rainfall for temperate deciduous or tropical rainforests.

A plain near the mountains. The climate is usual, +30..40 in July, -5..-10 in January, rains are... usual,  not a desert.

6 minutes ago, JoeSchmuckatelli said:

whereas in the Middle East and North Africa I've seen structures dating from before the Romans.

Did the Roman cow think that a hut made of its manure, food (straw), and clay will go through epochs when whole empires have gone.

[ARS]

So this is some scenes from T-34 movie (2018):

On 0:36, 0:52 and 2:42, we can see that a shell causes non-penetration/ ricochet on the tank's armor, with the side effect of causing a shock that makes the crew experiences what can be described as "my ears are ringing intensely". Is this true for real-life? This same effect that's experienced by tank crews when there's a non-penetration/ ricochet on their tank? Does modern tank have this effect too?

[TheSaint]

One of the effects that they aren't showing in those clips at all is spalling. When a round would strike hardened armor and fail to penetrate, it would many times cause large flakes of steel to fly off of the inside surface of the armor at high speed, possibly resulting in crew injury. Hearing loss was the least of their worries.

Although, interestingly, my father was a tanker in WWII, and he had severe hearing loss. (I was very used to being yelled at when I was a kid.) Mostly from the guns, although he was in a number of tanks when they were hit as well. I'm sure that didn't help.

Edited October 27, 2020 by TheSaint

[JoeSchmuckatelli]

4 hours ago, ARS said:

So this is some scenes from T-34 movie (2018):

On 0:36, 0:52 and 2:42, we can see that a shell causes non-penetration/ ricochet on the tank's armor, with the side effect of causing a shock that makes the crew experiences what can be described as "my ears are ringing intensely". Is this true for real-life? This same effect that's experienced by tank crews when there's a non-penetration/ ricochet on their tank? Does modern tank have this effect too?

So I'm a former tanker and yeah, getting shot sucks.  From what I have heard.  I've had a lot of near misses from arty and anti tank and anti air - which while better than the alternative does not give me first hand experience to answer. 

 

But I can say that as soon as tanks came on the scene - chainmail made a comeback!  The Brits in WWI found themselves in more danger from the spalling than from direct penetration. 

 

Nowadays we use Kevlar - but spalling is something we talk about. 

As far as the sound?  Well I'm pretty hard of hearing these days - and not that old.  Tanking is loud - as in being nearby while one is shooting is a whole-body experience.  Can literally take your breath away.  Ringing ears and headache?  You betcha! Knock you off your feet?  Uh huh (depends upon your experience and relative position and distance). 

 

So, yeah, old tanks with cast or rolled steel armor and no composite layers? 

 

Getting shot is gonna suck - presuming you are lucky enough to enjoy the suck. 

 

Edited October 27, 2020 by JoeSchmuckatelli

[JoeSchmuckatelli]

Inspired by @ARS's posts, here's a question for you materials science types:

 

Which is likely to be structurally stronger - an alloy or a composite / matrix? 

 

(I will permit any interpretation of 'stronger' to encourage discussion) 

[kerbiloid]

Composite/matrix.

1.  Carbon's enthalpy of vaporization is 50 kJ/kg, density 2.25 t/m³ , 50 * 2.25 ~= 112. 
While iron is 6 * 7.8 = 47, aluminium 10*2.7 = 27.
So, the theoretical upper limit of strength limit of carbon  is several times greater..
That's because of specific carbon bounds.

2. Alloys are casted, so they by definition contain crystal defects, while the composite theoretically can be monomolecular.

Edited November 1, 2020 by kerbiloid

[JoeSchmuckatelli]

The earth and moon are sometimes described as one orbiting the other, and sometimes as co-orbiting bodies with the barycenter inside the earth. 

 

So - if a small third body were to be captured in a virtually circular orbit outside of the moon's... Would the center of its orbit be the earth, or the barycenter of the earth - moon system - - or would its orbit be defined /shaped by the earth and moon separately? 

[magnemoe]

3 hours ago, JoeSchmuckatelli said:

The earth and moon are sometimes described as one orbiting the other, and sometimes as co-orbiting bodies with the barycenter inside the earth. 

 

So - if a small third body were to be captured in a virtually circular orbit outside of the moon's... Would the center of its orbit be the earth, or the barycenter of the earth - moon system - - or would its orbit be defined /shaped by the earth and moon separately? 

It would orbit the barycenter too, it had to be pretty far out so the moon did not alter it orbit much.

Here is pluto and its moons. 

[Shpaget]

A new barycenter would be established. Whether the additional body would significantly change the previous barycenter depends on the size  of the new body, but all bodies in a system contribute to the location of barycenter and all bodies orbit around it.

[K^2]

2 hours ago, magnemoe said:

It would orbit the barycenter too, it had to be pretty far out so the moon did not alter it orbit much.

Just want to add to this that it's not true for just any arrangement in general. 3-body dynamics can be very complex and nothing like orderly movement of bodies about common barycenter. But such systems are inherently unstable. Any stable star system or planetary system will, indeed, have bodies orbiting common barycenter. That typically means that at most two bodies are dominating the mass of the system.

As a point of interest, there are known stable arrangements of N-bodies orbiting common center, such as hexagonal variants of Klemperer Rosettes. But I can't imagine any natural process that would result in these, and even they do orbit a common barycenter.

[Shpaget]

Can someone check 1.1.1.1 DNS for me real quick?

I had it set up as my IPv4 DNS and today it borked. Setting my DNS as whatever my ISP wants it to be revived the connection to the interwebs, but https://www.cloudflarestatus.com says all is good and dandy.

Browsing to 1.1.1.1 doesn't seem to work either.

Thanks.

edit:

NVM, seems to work now.

Edited November 2, 2020 by Shpaget

[magnemoe]

On 11/1/2020 at 9:06 AM, K^2 said:

Just want to add to this that it's not true for just any arrangement in general. 3-body dynamics can be very complex and nothing like orderly movement of bodies about common barycenter. But such systems are inherently unstable. Any stable star system or planetary system will, indeed, have bodies orbiting common barycenter. That typically means that at most two bodies are dominating the mass of the system.

As a point of interest, there are known stable arrangements of N-bodies orbiting common center, such as hexagonal variants of Klemperer Rosettes. But I can't imagine any natural process that would result in these, and even they do orbit a common barycenter.

Yes I assumed the 3rd body was small compared to the other two as is case for Pluto. 

[ARS]

If there's a terrestrial planet with planet-wide storm (imagine Mars, but with it's global dust storm cranked up to eleven) that lasts indefinitely, assuming we have a reason to go down there and build something (doesn't have to be a colony, just an outpost or comms/sensor tower with skeleton crew is enough) where's the best region to choose in order to minimize the windspeed? Is it closer to equator or closer to poles? Does the storm gets stronger in poles or in equator? (Assume the entire planet is relatively featureless like those dead rockball moons with no high mountains or cliffs)

[Spacescifi]

4 hours ago, ARS said:

If there's a terrestrial planet with planet-wide storm (imagine Mars, but with it's global dust storm cranked up to eleven) that lasts indefinitely, assuming we have a reason to go down there and build something (doesn't have to be a colony, just an outpost or comms/sensor tower with skeleton crew is enough) where's the best region to choose in order to minimize the windspeed? Is it closer to equator or closer to poles? Does the storm gets stronger in poles or in equator? (Assume the entire planet is relatively featureless like those dead rockball moons with no high mountains or cliffs)

 

I would not go there at all.

But if it is anything like Earth...ever see how bad hurricanes and flooding damage the southwest USA?

That's near our equator by the way.

[K^2]

4 hours ago, ARS said:

If there's a terrestrial planet with planet-wide storm (imagine Mars, but with it's global dust storm cranked up to eleven) that lasts indefinitely, assuming we have a reason to go down there and build something (doesn't have to be a colony, just an outpost or comms/sensor tower with skeleton crew is enough) where's the best region to choose in order to minimize the windspeed? Is it closer to equator or closer to poles? Does the storm gets stronger in poles or in equator? (Assume the entire planet is relatively featureless like those dead rockball moons with no high mountains or cliffs)

If the planet rotates rapidly enough, poles are your best bet. If you have a global storm situation, you're likely to have two storm systems centered on either pole, with poles themselves, or some area nearby, acting as eye of a storm with relatively quiet weather. Beyond that, hard to say. On planets with high wind speeds, excluding the quiet area very close to the poles, polar regions are very turbulent, usually with a number of vortices forming a regular polygon around the pole. (Saturn's Hexagon) Closer to equator, you usually get bands of laminar and turbulent flows. Any of the laminar bands are fine to fly in, but might make it very difficult to land due to wind speeds. Whereas, ground wind speeds in turbulent areas might be reasonably low, but good luck flying in them. Some sort of transition region might exist that would allow you to approach and land, but it's hard for me to say for sure, and these are likely to be unstable, so having landed successfully, no guarantee you'll be able to take off shortly thereafter.

If planet's weather is not dominated by planet's rotation, you are likely to be looking at powerful storms at the terminator region with relatively quiet weather on the day and night sides. Unfortunately, temperatures there might be a problem. If the planet is not rotating rapidly enough to generate weather across its surface, then the day side is going to be very, very hot and night side very, very cold. Whether either of these prevents landing is going to depend on specifics. If the planet is close enough to the star, maybe night side is just fine for landing, and vice versa.

[SuperFastJellyfish]

11 hours ago, ARS said:

If there's a terrestrial planet with planet-wide storm (imagine Mars, but with it's global dust storm cranked up to eleven) that lasts indefinitely, assuming we have a reason to go down there and build something (doesn't have to be a colony, just an outpost or comms/sensor tower with skeleton crew is enough) where's the best region to choose in order to minimize the windspeed? Is it closer to equator or closer to poles? Does the storm gets stronger in poles or in equator? (Assume the entire planet is relatively featureless like those dead rockball moons with no high mountains or cliffs)

The axis of rotation probably affects this a lot.  If it's on its side like Uranus then it will vary by season where the storm is strongest, methinks.

[ARS]

If a tank is too heavy to cross a bridge, does widening the track to distribute the load over larger area helps to mitigate it? (Doesn't have to be moving fast, just cross the bridge, when deep fording isn't an option)

[kerbiloid]

The tar will be less damaged on the bridge fall.

[K^2]

4 hours ago, ARS said:

If a tank is too heavy to cross a bridge, does widening the track to distribute the load over larger area helps to mitigate it? (Doesn't have to be moving fast, just cross the bridge, when deep fording isn't an option)

Depends entirely on failure modes. I'm going to simplify a lot. Imagine a very simple bridge made from a framework of steel pipes welded together. The pipes form some sort of a grid on the top surface, so you placed wooden planks over these to make it into a bridge you can actually drive over. If the problem with the bridge is that the tank is breaking the planks, and then starts snapping individual pipes in the grid, then maybe wider track would distribute the weight better, and allow it to cross. But if the wood is holding, and some weld joints in the framework are giving out, then you probably just have too much total load on the bridge, and making tracks wider won't make any difference.

In practice it's a bit more complex than that, and it's always going to be some combination of both factors - total weight and weight distribution, but the key point remains. Depending on specific bridge construction and why it's failing, changing weight distribution might or might not help.

That said, I don't think there is any realistic situation where I knew there is a risk of bridge not surviving the crossing, me looking at the bridge and the tank, and saying, "Just make the tracks wider, and it will be fine." The fact that I expect bridge to fail in the former case suggests that even if I can improve the situation somewhat by changing weight distribution, the margin for safety is going to be just too narrow to be worth the risk. In the real world, there are always additional sources of stress and fatigue that you aren't aware of, and if you don't have a wide margin for these, it's just not worth it.

[magnemoe]

9 hours ago, K^2 said:

Depends entirely on failure modes. I'm going to simplify a lot. Imagine a very simple bridge made from a framework of steel pipes welded together. The pipes form some sort of a grid on the top surface, so you placed wooden planks over these to make it into a bridge you can actually drive over. If the problem with the bridge is that the tank is breaking the planks, and then starts snapping individual pipes in the grid, then maybe wider track would distribute the weight better, and allow it to cross. But if the wood is holding, and some weld joints in the framework are giving out, then you probably just have too much total load on the bridge, and making tracks wider won't make any difference.

In practice it's a bit more complex than that, and it's always going to be some combination of both factors - total weight and weight distribution, but the key point remains. Depending on specific bridge construction and why it's failing, changing weight distribution might or might not help.

That said, I don't think there is any realistic situation where I knew there is a risk of bridge not surviving the crossing, me looking at the bridge and the tank, and saying, "Just make the tracks wider, and it will be fine." The fact that I expect bridge to fail in the former case suggests that even if I can improve the situation somewhat by changing weight distribution, the margin for safety is going to be just too narrow to be worth the risk. In the real world, there are always additional sources of stress and fatigue that you aren't aware of, and if you don't have a wide margin for these, it's just not worth it.

Thinks tanks has pretty low ground pressure compared to heavy trucks because they are designed to be used off road. 
In short if an 60 ton truck can drive over an bridge so can an 60 ton tanks. 

I assume the issue with heavy load on bridges is max weight of vehicle at weakest point, on an simple beam bridge this will be center. 
Some weaker roads has limits to weight on axle as too heavy can damage the road, bridges tend to have max total weight rating. 

[DDE]

18 hours ago, ARS said:

If a tank is too heavy to cross a bridge, does widening the track to distribute the load over larger area helps to mitigate it? (Doesn't have to be moving fast, just cross the bridge, when deep fording isn't an option)

I doubt it, dispersing the weight over a mrginally greater area would only help preserve the surface of the bridge - it won't prevent the legs from snapping or the span of the bridge from collapsing. A tank long enough to distribute weight across several spans is not really an option.

Also partly relevant: it's a trap!

Spoiler

 

[kerbiloid]

An anti-tank, Or an antipod tank.

P.S.
Interesting fact. Actually, we see the Australian tanks like here.

Edited November 5, 2020 by kerbiloid