For Questions That Don't Merit Their Own Thread

[RainDreamer]

So my brother and I were talking recently about medieval warfare and the application of modern knowledge to create medieval war weapons, and I thought of using charcoal dust to create medieval fuel air bombs. Does it sound plausible? Has it been used in history?

I am still figuring a deployment method, like catapult launching charcoal dust bags, with the seams tied to weights. In mid air, the rotation of the bags and the weights will cause stress to the seam and cause it to rip, dispersing the charcoal dust over an area. When that dust cloud reach the torch lighting inside a medieval castle, for example, or ignited with following fire arrows, it would cause a thermobaric explosion, wouldn't it?

[MinimumSky5]

The dust would need to be very finely ground, and if it was released in mid air it would likely disperse before becoming explosive, just having a fairly weak bag rupture on impact might be enough to create an explosive mixture.

[HoloYolo]

Why does salt cause water to freeze at a lower temperature? Is it because there is more to freeze?

[MinimumSky5]

Why does salt cause water to freeze at a lower temperature? Is it because there is more to freeze?

The sodium and chlorine ions disrupt the forming ice crystals, meaning that the water molecules have to be moving more slowly to be incorporated into the structure.

[windows_x_seven]

Do all gases expand the same when heated?

Let's say I filled a balloon with Nitrogen and another balloon with Helium, both with the same starting volume and temperature, and then start heating them to a certain temperature.

Would one of these gases expand more than the other?

[peadar1987]

Do all gases expand the same when heated?

Let's say I filled a balloon with Nitrogen and another balloon with Helium, both with the same starting volume and temperature, and then start heating them to a certain temperature.

Would one of these gases expand more than the other?

Yes. All materials have different coefficients of thermal expansion. Hang on a sec and I'll find an exact answer to your question...

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So if you have a balloon of helium and a balloon of nitrogen at room temperature and pressure, and heat them up to 100 celsius, the helium will expand by 25%, and the nitrogen will expand by 25.48%, whereas the helium will expand by 25.435%. So not a big difference, but there is one.

[KSK]

Do all gases expand the same when heated?

Let's say I filled a balloon with Nitrogen and another balloon with Helium, both with the same starting volume and temperature, and then start heating them to a certain temperature.

Would one of these gases expand more than the other?

According to the ideal gas law - no. This treats the gas molecules ( or atoms in the case of helium) as point particles which don't interact. Clearly this is not the case otherwise gases would never liquify.

The van der Waals equation is more accurate and includes empirical terms to take account of molecular size and the forces between them. It's a better approximation but only within a certain range of pressures and temperatures. It predicts that the helium should expand slightly more. Nitrogen molecules are larger and so the attractive (van der Waals) forces between them are higher, so for a given pressure and temperature a mole of nitrogen should occupy less volume than a mole of helium.

In practice, the difference is so small that you probably wouldn't notice any difference in balloon size.

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So my brother and I were talking recently about medieval warfare and the application of modern knowledge to create medieval war weapons, and I thought of using charcoal dust to create medieval fuel air bombs. Does it sound plausible? Has it been used in history?

I am still figuring a deployment method, like catapult launching charcoal dust bags, with the seams tied to weights. In mid air, the rotation of the bags and the weights will cause stress to the seam and cause it to rip, dispersing the charcoal dust over an area. When that dust cloud reach the torch lighting inside a medieval castle, for example, or ignited with following fire arrows, it would cause a thermobaric explosion, wouldn't it?

Not sure about charcoal but flour can be very dangerous for that reason. I've read that it used to be a big danger in medieval mills (where lighting options were limited and usually involved flames) and even today, it's by no means something that the modern day food industry can ignore.

Edited August 9, 2015 by KSK

[RainDreamer]

Can you sanitize something made from glass by popping it in the microwave for like 5 minutes? The waves wouldn't effect bacteria and the like that much, would it? Edit: the object in question is slightly wet, since I don't think microwave works on dry glass.

Edited August 11, 2015 by RainDreamer

[shynung]

Can you sanitize something by popping it in the microwave for like 5 minutes? The waves wouldn't effect bacteria and the like that much, would it?

Microwave ovens heat anything with water in it, so, maybe.

[Dkmdlb]

How much does the water recovery equipment aboard the ISS weigh?

[K^2]

Microwave ovens heat anything with water in it, so, maybe.

They will heat a lot of things. They are designed to be particularly effective with water, but there aren't a lot of things that you flat out can't heat up.

That said, if your goal is to heat up a bowl, put water in it. It will not only absorb microwaves, but also help heat the bowl more efficiently, and prevent it from overheating.

On that note, always be careful heating pure water in a smooth glass container in microwave. It's very easy to superheat the liquid, causing it to be above 100°C without boiling. In this case, sinceall you care aobut is heating the container, add something with the rough surface into the bowl with water. It will work like a boiling cork, preventing superheating. Water will just boil normally instead.

And yeah, if you get it to boiling temperature, and give it a few minutes, it a good way to sterilize something. Very few bacteria can survive both room temperature and boiling water.

[shynung]

They will heat a lot of things. They are designed to be particularly effective with water, but there aren't a lot of things that you flat out can't heat up.

That said, if your goal is to heat up a bowl, put water in it. It will not only absorb microwaves, but also help heat the bowl more efficiently, and prevent it from overheating.

On that note, always be careful heating pure water in a smooth glass container in microwave. It's very easy to superheat the liquid, causing it to be above 100°C without boiling. In this case, sinceall you care aobut is heating the container, add something with the rough surface into the bowl with water. It will work like a boiling cork, preventing superheating. Water will just boil normally instead.

And yeah, if you get it to boiling temperature, and give it a few minutes, it a good way to sterilize something. Very few bacteria can survive both room temperature and boiling water.

So, according to your info, I'd say putting the object in a large glass bowl of water should sterilize it.

Though, what if there isn't much water? Say, just dipped in water, then microwaved for a few minutes?

[andrewas]

No, a thin film of water will evaporate before doing much good. Depending on what the object is made of, that might leave nothing in the chamber to absorb the microwaves, which can damage the oven. You need to the objects surface to 100C for a few minutes, which means you need a substantial amount of water.

[magnemoe]

They will heat a lot of things. They are designed to be particularly effective with water, but there aren't a lot of things that you flat out can't heat up.

That said, if your goal is to heat up a bowl, put water in it. It will not only absorb microwaves, but also help heat the bowl more efficiently, and prevent it from overheating.

On that note, always be careful heating pure water in a smooth glass container in microwave. It's very easy to superheat the liquid, causing it to be above 100°C without boiling. In this case, sinceall you care aobut is heating the container, add something with the rough surface into the bowl with water. It will work like a boiling cork, preventing superheating. Water will just boil normally instead.

And yeah, if you get it to boiling temperature, and give it a few minutes, it a good way to sterilize something. Very few bacteria can survive both room temperature and boiling water.

I remember superheated water once, someone was heating water for tee or coffee in the microwave. Nothing then an poof sound and the cup was almost empty

I guess the water got super-heated then switched state to boiling explosively and the steam pushed most of the water out of the cup.

[RainDreamer]

How do rocket engine testing facilities absorb all that force from a rocket engine blasting at full throttle? Seems like even the testing facilities for them are marvels of engineering themselves.

[Kryten]

It's not that much force as things go; even the largest engines have thrust forces within what an average building would be dealing with anyway. If you mean the exhaust, that's usually just directed into an earth or concrete berm.

[Mazon Del]

I wouldn't say "an average" building could withstand those forces. That said, it is mostly a matter of ensuring a good foundation (big and certain vibration resistant cement mixes) and thick enough struts (heh). Some effort sure, but not exactly anything too special.

[peadar1987]

If you think about the force, the Saturn V had 5 F-1 engines on the first stage, which gave it a TWR of about 1.1 (IIRC). One F-1 engine would produce enough thrust to lift about 1/5 of the mass of a Saturn V, so if something could hold 1/5 of the mass of the rocket (3,000,000kg/6=500,000kg), it could hold an F-1 at full thrust.

[Camacha]

How do rocket engine testing facilities absorb all that force from a rocket engine blasting at full throttle? Seems like even the testing facilities for them are marvels of engineering themselves.

Water. Water dampens the bejeebies out of shockwaves. It is not just there to extinguish, it is mostly meant for dampening.

Edited August 18, 2015 by Camacha

[hugix]

Why isn't the Atlas LV-3B (used during the Mercury orbital missions) considered a SSTO? Technically it is. It was a single staged rocket that got the Mercury capsule into orbit. That means that the entire launch stack (Atlas rocket + payload) was in orbit just between MECO and speration of capsule.

Which is technically the definition of a Single Stage To Orbit. True, it doesn't return from orbit. But a vehicle that returns in one piece should be called a SSTOAB (Single Stage To Orbit And Back)

[Kryten]

Why isn't the Atlas LV-3B (used during the Mercury orbital missions) considered a SSTO? Technically it is. It was a single staged rocket that got the Mercury capsule into orbit. That means that the entire launch stack (Atlas rocket + payload) was in orbit just between MECO and speration of capsule.

Atlas (at least the orbital versions) was still staged, it dropped a pair of boost engines.

[hugix]

Atlas (at least the orbital versions) was still staged, it dropped a pair of boost engines.

I know some Atlas rockets dropped engines but I did not know these LV-3B rockets did that also. do you have any more info on it? Since there isn't anything on the boost engines on wikipedia https://en.wikipedia.org/wiki/Atlas_LV-3B

[Kryten]

I know some Atlas rockets dropped engines but I did not know these LV-3B rockets did that also. do you have any more info on it? Since there isn't anything on the boost engines on wikipedia https://en.wikipedia.org/wiki/Atlas_LV-3B

Here's a good general overview;

http://www.b14643.de/Spacerockets/Diverse/Atlas_MA-drive-system/index.htm

all Atlases after the experimental Atlas-A (X-11) until Atlas III (introduced RD-180) used the staged engine.

[MinimumSky5]

All Atlas boosters, launch vehicles and missiles used the stage and a half design until the Atlas III launch vehicle in 2000. The article lists things that changed between the SM-65 Atlas and the Atlas LV-3B, anything else probably didn't change.

[More Boosters]

Is it possible to have a neutron star system with the satellites all in stable orbits? If so what would such a planet look like, how would it differ from your everyday good old yellow generic MS star system, and how would the satellites be affected? What would be the constraints for planets if there are to be any unique ones? What would the star look like to an observer that stands on the surface of a satellite? Pushing it further, is it possible to have a habitable planet around a neutron star?