Fun Fact Thread! (previously fun fact for the day, not limited to 1 per day anymore.)

[kerbiloid]

In 1654 they were trying to pull off the hemispeheres.

Spoiler

300 years later they were pushing them back.

Spoiler

 

[magnemoe]

On 6/11/2024 at 4:54 PM, kerbiloid said:

In 1654 they were trying to pull off the hemispeheres.

  Reveal hidden contents

300 years later they were pushing them back.

  Hide contents

 

That looks a lot like an cutaway fatman nuke.  Imagine the exposed screws on the bottom explains it poor accuracy,  and don't see their reason unless you are supposed to put this thing of the top of an small rocket  

Counter with another one: You know the north star changes because the earth axis moves so the ancient Egyptians had another north star than us.  
Sharks are older than the current north star, not related to shifting of the axis they are older than an very well know star. 

[JoeSchmuckatelli]

1 hour ago, magnemoe said:

Sharks are older than the current north star, not related to shifting of the axis they are older than an very well know star

Obligatory quibble:

Sharks are not older than the North star - but they are older than the star being North. 

I think I get 2 @kerbiloid points for that one! 

[farmerben]

Correcting one of my mistakes on a lost thread:

There is some evidence of communication between the ancient Polynesia and the Americas.  The sweet potato is thought to have originated in South America and made it to the Pacific Islands.  

[kerbiloid]

12 hours ago, magnemoe said:

That looks a lot like an cutaway fatman nuke. 

A Fallout Fatman nuke, based on the Mk3 Fatman nuke.

***

The human history is just a short episode of the endless shark drama.

[AckSed]

Hannover Institute of Technology has an Einstein Elevator, a micro-gravity drop tower that encloses the vacuum in a small shell and then lifts it: https://www.hitec.uni-hannover.de/en/large-scale-equipment/einstein-elevator/

[Nuke]

On 6/15/2024 at 6:06 PM, magnemoe said:

That looks a lot like an cutaway fatman nuke.  Imagine the exposed screws on the bottom explains it poor accuracy,  and don't see their reason unless you are supposed to put this thing of the top of an small rocket  

Counter with another one: You know the north star changes because the earth axis moves so the ancient Egyptians had another north star than us.  
Sharks are older than the current north star, not related to shifting of the axis they are older than an very well know star. 

thats not the fatman tail though, i think the original had box fins.

[magnemoe]

5 hours ago, AckSed said:

Hannover Institute of Technology has an Einstein Elevator, a micro-gravity drop tower that encloses the vacuum in a small shell and then lifts it: https://www.hitec.uni-hannover.de/en/large-scale-equipment/einstein-elevator/

Sounds like they don't drop it in vacuum but rather uses motors to compensate for drag, hard but you know the drag and the weigh of the capsule and huge vacuum chambers are expensive to run. 
You can remove the air from the capsule if needed. 

[kerbiloid]

On 6/19/2024 at 6:30 PM, Nuke said:

thats not the fatman tail though, i think the original had box fins.

It has a rule in foot's to the right, with a huge clip.

[kerbiloid]

_{(From https://pikabu.ru/story/iz_chego_zhe_iz_chego_zhe_iz_chego_zhe_nozhi_iz_raznogo_11526690)}

A really important study.
I believe, Mark Watney could apply this knowledge if he knew.

https://www.sciencedirect.com/science/article/pii/S2352409X19305371

also

Spoiler

 

 

[Codraroll]

I just thought of a fun-ish story from my (admittedly not very long) academic career. Sometimes, the most innocuous questions turn out to be the hardest to answer. In my case, it was as simple as "I need to do some back-of-the-envelope calculations. What's a suitable value for the thermal conductivity (λ value) of snow?" That was a rabbit hole. Snow is flipping impossible to examine theoretically.

Okay, I might as well explain the context too. Like everything fluffy that contains air, snow has rather good insulating properties. That means there will be a temperature gradient through a snowdrift accumulated on a roof. If you consider the roof-with-snow as the building envelope, you've got the indoors temperature on one side, the outdoors temperature on the other side, and the temperature in-between is something in-between. If the outdoors temperature is right below the freezing point, the temperature inside the snowdrift can theoretically reach above (although in practice it will of course not exceed) 0 °C. That's the point where snow begins to melt. The snowmelt runs off the roof, and since the outdoors temperature is below freezing, it will re-form into icicles and be a hazard to passers-by on the street below. My simple question as a building scientist was thus how much snow needs to accumulate on the roof before that can happen. It's a very simple calculation in principle; all you need is the thermal conductivity of the snowdrift.

And then I found that the estimates for that thermal conductivity spanned roughly two orders of magnitude. They range from λ = 0.06 W/mK to λ = 3.6 W/mK. That gives the calculation a margin of error of thousands of percent, making it not a very useful one. So why is this so difficult?

As we all know, a snowflake is a pretty, tiny ice crystal. But snow in bulk is a mixture of ice (λ = 2-3.6 W/mK), air (λ = 0.02 W/mK), and liquid water (λ = 0.6 W/mK). The ratio between the three ingredients depends on all sorts of factors, including the temperature during the snowfall, the air humidity, the rate of snowfall, and wind. Of course, two of the ingredients frequently turn into each other and back. As snow builds up, it compresses under its own weight, changings its porosity, and hence its density. As it melts, it soaks up its own melt water like a sponge. It can partially melt and re-freeze; in fact it does so all the time. After all, it's a material that can only form at temperatures close to that of its phase transition. A deeper snowdrift will consist of many different layers of snow, each with a different composition and possibly a different structure. And of course, the thickness of the snowdrift and/or the individual layers changes as the snow compresses and/or melts. Exposure to sun and/or wind will of course mess things up too. And there's probably even more stuff that plays in to change the thermal conductivity.

In fact, you can't even measure it reliably. All the standard methods involve creating a thermal gradient through the material, and you can't do that without either melting some of the ice or freezing some of the water - which will also change the porosity of the snow. You can't measure the porosity and the water content of the same sample either. The best you can do is putting some thermometers below and on top of the snow drift and do some calculations based on their readings, but you can't insert them into an existing snowdrift without disturbing its structure.

And any thermal simulations that involve snow will necessarily have to include a dynamic thermal conductivity, dynamic layer thicknesses, account for the energy required to undergo phase transitions, and deal with liquid water and capillary action. Of course, the capillary properties also change as the snow melts and freezes, so good luck with that bit. Not to mention that most simulation algorithms just throw their proverbial hands up when liquid water appears. Snow really is a material that hates being simulated.

What I ended up with was making some assumptions (λ = 0.16 W/mK, based on some work by an American meteorologist back in the 90's), but they proved rather difficult to test in practice. The best guess is "you'll start seeing some icicles if you have more than 10 cm of snow and temperatures right below zero on a roof insulated to the building code specifications", but heck if I know whether that's correct in general terms. I guess one just has to wait through several winters to see. But then you're likely to just find an answer that works for one specific roof in one specific climate.

[darthgently]

2 hours ago, Codraroll said:

I just thought of a fun-ish story from my (admittedly not very long) academic career. Sometimes, the most innocuous questions turn out to be the hardest to answer. In my case, it was as simple as "I need to do some back-of-the-envelope calculations. What's a suitable value for the thermal conductivity (λ value) of snow?" That was a rabbit hole. Snow is flipping impossible to examine theoretically.

Okay, I might as well explain the context too. Like everything fluffy that contains air, snow has rather good insulating properties. That means there will be a temperature gradient through a snowdrift accumulated on a roof. If you consider the roof-with-snow as the building envelope, you've got the indoors temperature on one side, the outdoors temperature on the other side, and the temperature in-between is something in-between. If the outdoors temperature is right below the freezing point, the temperature inside the snowdrift can theoretically reach above (although in practice it will of course not exceed) 0 °C. That's the point where snow begins to melt. The snowmelt runs off the roof, and since the outdoors temperature is below freezing, it will re-form into icicles and be a hazard to passers-by on the street below. My simple question as a building scientist was thus how much snow needs to accumulate on the roof before that can happen. It's a very simple calculation in principle; all you need is the thermal conductivity of the snowdrift.

And then I found that the estimates for that thermal conductivity spanned roughly two orders of magnitude. They range from λ = 0.06 W/mK to λ = 3.6 W/mK. That gives the calculation a margin of error of thousands of percent, making it not a very useful one. So why is this so difficult?

As we all know, a snowflake is a pretty, tiny ice crystal. But snow in bulk is a mixture of ice (λ = 2-3.6 W/mK), air (λ = 0.02 W/mK), and liquid water (λ = 0.6 W/mK). The ratio between the three ingredients depends on all sorts of factors, including the temperature during the snowfall, the air humidity, the rate of snowfall, and wind. Of course, two of the ingredients frequently turn into each other and back. As snow builds up, it compresses under its own weight, changings its porosity, and hence its density. As it melts, it soaks up its own melt water like a sponge. It can partially melt and re-freeze; in fact it does so all the time. After all, it's a material that can only form at temperatures close to that of its phase transition. A deeper snowdrift will consist of many different layers of snow, each with a different composition and possibly a different structure. And of course, the thickness of the snowdrift and/or the individual layers changes as the snow compresses and/or melts. Exposure to sun and/or wind will of course mess things up too. And there's probably even more stuff that plays in to change the thermal conductivity.

In fact, you can't even measure it reliably. All the standard methods involve creating a thermal gradient through the material, and you can't do that without either melting some of the ice or freezing some of the water - which will also change the porosity of the snow. You can't measure the porosity and the water content of the same sample either. The best you can do is putting some thermometers below and on top of the snow drift and do some calculations based on their readings, but you can't insert them into an existing snowdrift without disturbing its structure.

And any thermal simulations that involve snow will necessarily have to include a dynamic thermal conductivity, dynamic layer thicknesses, account for the energy required to undergo phase transitions, and deal with liquid water and capillary action. Of course, the capillary properties also change as the snow melts and freezes, so good luck with that bit. Not to mention that most simulation algorithms just throw their proverbial hands up when liquid water appears. Snow really is a material that hates being simulated.

What I ended up with was making some assumptions (λ = 0.16 W/mK, based on some work by an American meteorologist back in the 90's), but they proved rather difficult to test in practice. The best guess is "you'll start seeing some icicles if you have more than 10 cm of snow and temperatures right below zero on a roof insulated to the building code specifications", but heck if I know whether that's correct in general terms. I guess one just has to wait through several winters to see. But then you're likely to just find an answer that works for one specific roof in one specific climate.

Water and its properties, in all its phases and forms is mind-boggling.  While when younger I thought otherwise, now I'm not surprised that we cannot thermally model a few cubic meters of snow on  some square meters of roof. 

We, as a culture, put far too much faith (no better word for it) in computer models. 

The PBS inspired meme  The More You Know!  would be more wisely put  The More You Admit You Don't Know!

And The Science is Settled  would be better as  Science, by definition, is Unsettling

[JoeSchmuckatelli]

11 hours ago, Codraroll said:

question as a building scientist

I enjoyed your story! 

I started reading a bunch of the work put out by a Canadian building scientist (can't remember name offhand) back 20 some odd years ago.  Was fascinating to watch them try to figure out 'the perfect wall' and answer the insulation, vapor barrier and construction practices questions I was wrestling with.  (At the time I was trying to help a client design and build a high efficiency addition using the latest practices) 

Looks like a. Cool field! 

[StrandedonEarth]

9 hours ago, darthgently said:

Water and its properties, in all its phases and forms is mind-boggling. 

Considering that the Inuit have a dozen or so base words for snow and ice, which can be affixed to form 50 or so, including general words that include snow...

https://www.thecanadianencyclopedia.ca/en/article/inuktitut-words-for-snow-and-ice

[darthgently]

37 minutes ago, StrandedonEarth said:

Considering that the Inuit have a dozen or so base words for snow and ice, which can be affixed to form 50 or so, including general words that include snow...

https://www.thecanadianencyclopedia.ca/en/article/inuktitut-words-for-snow-and-ice

I gather the form of water ice crystals on earth are apparently quite rare in the solar system.  Most ice out there is apparently non-crystalline and is polymorphic, or glasslike, instead.  I probably have the terminology off.  Then there are other crystalline patterns H2O can take other than what we see on earth (6-symmetry, snowflakes, etc).  Vonnegut's Ice-9 comes to mind, lol

[Codraroll]

13 hours ago, JoeSchmuckatelli said:

I enjoyed your story! 

I started reading a bunch of the work put out by a Canadian building scientist (can't remember name offhand) back 20 some odd years ago.  Was fascinating to watch them try to figure out 'the perfect wall' and answer the insulation, vapor barrier and construction practices questions I was wrestling with.  (At the time I was trying to help a client design and build a high efficiency addition using the latest practices) 

Looks like a. Cool field! 

Definitely a cool field! I was drawn to it because it's a very practical subject with lots of everyday applications. I mean, practically everybody is involved on the user side of building science. The international research community is surprisingly small, though. Outside of the Nordic countries, few have even heard about building physics as a discipline (it doesn't even have a Wikipedia page), and the subject of moisture in buildings is mostly only studied in northern Europe. I don't think even the UK has an active research community working on building moisture, which is kind of strange considering it's the primary degradation mechanism for all buildings that feature organic materials or experience freeze-thaw cycles. Anywhere you go in the world you find institutes researching building energy use, or sustainability, but mention degradation (outside the context of preserving historic architecture) and you just get funny looks. It's almost so I'm asking whether buildings even degrade in those climates, or if they just accept it as a default fact of life.

[darthgently]

31 minutes ago, Codraroll said:

Definitely a cool field! I was drawn to it because it's a very practical subject with lots of everyday applications. I mean, practically everybody is involved on the user side of building science. The international research community is surprisingly small, though. Outside of the Nordic countries, few have even heard about building physics as a discipline (it doesn't even have a Wikipedia page), and the subject of moisture in buildings is mostly only studied in northern Europe. I don't think even the UK has an active research community working on building moisture, which is kind of strange considering it's the primary degradation mechanism for all buildings that feature organic materials or experience freeze-thaw cycles. Anywhere you go in the world you find institutes researching building energy use, or sustainability, but mention degradation (outside the context of preserving historic architecture) and you just get funny looks. It's almost so I'm asking whether buildings even degrade in those climates, or if they just accept it as a default fact of life.

Not to mention the health issues when there is not enough air exchange and high moisture.  The dreaded black mold

[kerbiloid]

The first attempt of building an igloo by the academic scientists failed due to the absence of reference table with snow conductivity.

[Codraroll]

9 hours ago, darthgently said:

Not to mention the health issues when there is not enough air exchange and high moisture.  The dreaded black mold

For whatever reason, matters of air quality usually goes into the hands of the ventilation people. Building physics, at least as it's practiced in the Nordic countries, is about preventing fungal growth inside the building structure itself, often from the outside.

3 hours ago, kerbiloid said:

The first attempt of building an igloo by the academic scientists failed due to the absence of reference table with snow conductivity.

Ironically enough, doing thermal calculations that involve only snow is trivial. Your temperature will be 0 °C or colder. The question is how long the structure lasts.

[kerbiloid]

6 hours ago, Codraroll said:

Ironically enough, doing thermal calculations that involve only snow is trivial. Your temperature will be 0 °C or colder. The question is how long the structure lasts.

Until the temperature gets 0 °C or warmer, n'est-ce pas?

6 hours ago, Codraroll said:

Building physics, at least as it's practiced in the Nordic countries, is about preventing fungal growth inside the building structure itself, often from the outside.

At the temperature of 0 °C or colder the fungi don't grow.

Combo!

[Superfluous J]

On 6/10/2024 at 2:33 PM, Beamer said:

Cleopatra was born closer in time to the moon landings than to the building of the Great Pyramid.

I was born closer to (some of) the time period Downton Abbey is in, than today.

[kerbiloid]

I was born in the middle between the first Sputnik and Space Shuttle, so feeling hanged between the epochs.

[JoeSchmuckatelli]

Wine - Dinosaur link discovered 

https://www.telegraph.co.uk/world-news/2024/07/01/demise-of-dinosaurs-allowed-vines-to-thrive-find-scientists/

 

[darthgently]

14 minutes ago, JoeSchmuckatelli said:

Wine - Dinosaur link discovered 

https://www.telegraph.co.uk/world-news/2024/07/01/demise-of-dinosaurs-allowed-vines-to-thrive-find-scientists/

 

Maybe also allowed some meek tree-dwelling lemur-like creatures to have more and bigger trees to flourish within and hatch their plan to rule the world and thence the stars!

[magnemoe]

On 6/21/2024 at 5:44 PM, kerbiloid said:

_{(From https://pikabu.ru/story/iz_chego_zhe_iz_chego_zhe_iz_chego_zhe_nozhi_iz_raznogo_11526690)}

A really important study.
I believe, Mark Watney could apply this knowledge if he knew.

https://www.sciencedirect.com/science/article/pii/S2352409X19305371

also

  Reveal hidden contents

 

 

I call that an obvious tall tale, an ax would make more sense but you could not keep an edge for cutting skin. 
If the rest of story is true, my guess he stole an knife and did not want to admit it, he could also made an knife but then why not say or or even show it.