For Questions That Don't Merit Their Own Thread

[magnemoe]

On 30.10.2016 at 9:34 AM, Green Baron said:

I guess the same :-)

I never flew helicopters, but from what i heard It's "difficult" to hover a helicopter stationary just above ground because it partly "floats" on compressed air. To illustrate this, imagine there is only one point on top where it is stable and the pilot has to counteract any tendencies to "slide off" from this point.

Furthermore, no part must touch the ground when the helicopter floats. When the gear touches the ground and is held (e. g. by gras) while the helicopter floats (moves) the gyro forces will cause it to flip.

 

Its an famous picture of an huge helicopter in Afghanistan who has touched down lightly with the rear part on the roof of an house, yes it might apply some ton pressure and the pilot was an expert. 

[Magzimum]

Is there a definition of a moon or natural satellite - especially, is there a size minimum? 

I was reading up a little on wikipedia on moons in our solar system (the real one), but couldn't find what would be a minimum size for something to be called a natural satellite or moon. I am assuming that the billions of dust particles of Saturn are not all moons - or at least not counted on the wiki page. But the moons of Mars are just large rocks, and they are considered moons. So where's the limit? 

Shocking btw to read how much stuff is orbiting other planets/dward planets in our solar system. It numbers in the hundreds of objects!

[Green Baron]

The IAU gives a definition of a planet or dwarf planet. A moon then is a natural satellite that orbits a planet or dwarf planet. This is a little fuzzy when it comes to bodies of similar size, but as Phoebos and Deimos are Mars' moons likewise Charon is a moon of Pluto.

I suppose there is no minimum size, the special case being that two bodies are equal in mass ...

 

[Tullius]

In the wikipedia article you linked, it is stated:

Quote

There is no established lower limit on what is considered a "moon". Every natural celestial body with an identified orbit around a planet of the Solar System, some as small as a kilometer across, has been considered a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets. Small asteroid moons (natural satellites of asteroids), such as Dactyl, have also been called moonlets.

Not really precise, but probably as precise as it gets, since astronomers probably did not yet bother giving a precise definition, since no one has started a catalogue of all the objects in Saturns rings.

[Wjolcz]

How did MESSENGER use gravity assists to decrease it's aphelion and perihelion? The only way to do that I can think of is encountering a planet from the leading side (front/prograde) and then let it pull you back, thus decreasing your Pe?

Edited November 15, 2016 by Veeltch

[p1t1o]

1 hour ago, Veeltch said:

How did MESSENGER use gravity assists to decrease it's aphelion and perihelion? The only way to do that I can think of is encountering a planet from the leading side (front/prograde) and then let it pull you back, thus decreasing your Pe?

I think that is precisely it.

[Aghanim]

In Legend of Korra, spirits states that there is this thing called "harmonic convergence" where all planets in their solar system are aligned in each other and spiritual thingies starts to happen. My question is that is it possible that all planets in our solar system align together, when does it happen, and how do we calculate it?

Edited November 15, 2016 by Aghanim

[peadar1987]

2 hours ago, Aghanim said:

In Legend of Korra, spirits states that there is this thing called "harmonic convergence" where all planets in their solar system are aligned in each other and spiritual thingies starts to happen. My question is that is it possible that all planets in our solar system align together, when does it happen, and how do we calculate it?

It's theoretically possible, but extremely unlikely. This page gives a pretty good overview of it all, better than I could anyway: http://www.mathpages.com/home/kmath161/kmath161.htm

[Aghanim]

So basically this would not happen?

[kerbiloid]

Is there a proper name in English for such kind of a picture, to search?

Spoiler

I.e. not a 3d view, but flat, not rotated, cut along to see intestines.

"Blueprint" and "cutout" usually give either 3d view or any schematic picture.

Edited November 16, 2016 by kerbiloid

[p1t1o]

1 hour ago, kerbiloid said:

Is there a proper name in English for such kind of a picture, to search?

  Reveal hidden contents

I.e. not a 3d view, but flat, not rotated, cut along to see intestines.

"Blueprint" and "cutout" usually give either 3d view or any schematic picture.

Try these: "Plan view", "Line drawing", "Cross section"

[TheEpicSquared]

So I want to make a rocket, but I can't find potassium nitrate anywhere. Then I saw a video where celluloid (aka the stuff ping pong balls are made of) was used to make a small rocket. However the video wasn't very clear and I'm not sure if it really was ping pong ball stuff. So my question is, would celluloid (maybe in powdered form) work as an oxidizer for a solid fuel rocket if mixed with sugar? 

Thanks  

[p1t1o]

38 minutes ago, TheEpicSquared said:

So I want to make a rocket, but I can't find potassium nitrate anywhere. Then I saw a video where celluloid (aka the stuff ping pong balls are made of) was used to make a small rocket. However the video wasn't very clear and I'm not sure if it really was ping pong ball stuff. So my question is, would celluloid (maybe in powdered form) work as an oxidizer for a solid fuel rocket if mixed with sugar? 

Thanks  

Celluloid is made from nitrocellulose - otherwise known as guncotton - which is a low-order explosive, it contains fuel and oxidiser elements.

Celluloid is treated to reduce flammability, so Im not sure how you would go about making a rocket from the stuff, but it certainly contains some energy, but I think it might be a little more involved than "use it as an oxidiser" - it may be suitable as a propellant on its own if prepared properly.

 

The only concrete advice that it is sensible for me to give is - be *extremely* careful and only proceed after receiving *actual* expert advice from someone who has handled the stuff in this way before. Even though celluloid is less sensitive than raw nitrocellulose, it is still known for being flammable, and has caused several accidents in the past. 

And "powdering" it will significantly increase the risk of a spontaneous ignition or *explosion* - this is not an exagerration - again get expert advice when doing anything with rocket fuels or explosives. If you have a local "rocketry club" or something similar, that would probably be a good place to start, I wouldn't recommend getting instructions solely from the internet.

 

***

 

On a lighter note: if you havn't already, read this: https://library.sciencemadness.org/library/books/ignition.pdf

[TheEpicSquared]

@p1t1o Damn I had no idea it was so dangerous.  We'll (my friend and I) talk it over with our teacher. Thanks for the info.  

[K^2]

On 11/18/2016 at 0:45 AM, TheEpicSquared said:

So I want to make a rocket, but I can't find potassium nitrate anywhere. Then I saw a video where celluloid (aka the stuff ping pong balls are made of) was used to make a small rocket. However the video wasn't very clear and I'm not sure if it really was ping pong ball stuff. So my question is, would celluloid (maybe in powdered form) work as an oxidizer for a solid fuel rocket if mixed with sugar?

Ok, so first of all, any rocket engine you build is a potential explosive. If you can't make sure you will be safe under assumption that it can explode at absolutely any moment, including while being made, simply sitting on your desk, or while you are trying to ignite it, then don't do it.

Second, the safety of an engine is primarily due to materials and size. One gram of nitrocellulose in a closed hand can sever a finger. And unlike some other options for rocket engines, it can explode even without an enclosure. I would avoid it. With enclosure, things become even more dangerous. After explosion, it becomes shrapnel. Never use metal. Cardboard is least bad, but can still do damage.

If you live in US, the reason you can't find potassium nitrate is because it's on the ATF list as an explosives ingredient. While you can still obtain it, any rocket motor you make with it will be an explosive device according to US federal law. Sugar motors are technically legal to make, but it's illegal to transport them without a license, so even just taking it from your home to a place you will launch it could be a felony under federal law. Many other countries have similar restrictions, so check before you make something like this.

For safety and avoiding legal complications, best option is to do what NASA does and go with APCP. It is less volatile, has better performance, and as far as I know, won't put you onto any gov't watch-list. On the other hand, it's still a rocket motor, so when these things do explode, they explode well. And while not in as much of a legal limbo, ammonium perchlorate is still not trivial to obtain. Which is probably for the best.

Hopefully, all of the above is sufficient to talk you out of it. If not, maybe it will at least help you to keep your fingers and eyes and keep you out of jail.

[p1t1o]

19 hours ago, TheEpicSquared said:

@p1t1o Damn I had no idea it was so dangerous.  We'll (my friend and I) talk it over with our teacher. Thanks for the info.  

No worries, at least you came to ask about it in the right place

Good idea to talk to your teacher, @K^2 reinforces the safety and also the legislative side, but ask your (science?) teacher if perhaps they can arrange a demonstration (if your school is equipped with rudimentary lab facilities?) - at my school we occasionally did things like this. At the very least it should be easy for a school science department to get small amounts of various materials and demonstrate some of their properties.

 

[Tullius]

It depends on your teacher. My brother once produced nitrocellulose in school. So it can't be that dangerous.

Even though it was under the supervision of teachers that produced themself nitroglycerine (the more dangerous brother of nitrocellulose) to put it into tiny tubes. And we students were allowed to hold those into a flame. Suffice to say that wearing safety goggles was essential, since even though they were only tiny droplets of nitroglycerine, you could feel the glass fragments on your skin from 1 meter away.

So it depends on how much your teacher trusts you and how well your school is equipped (my school was very well equipped).

[p1t1o]

**EDIT**

I'll just leave this here: http://www.mirror.co.uk/news/world-news/student-killed-another-injured-after-7693421

***********

1 hour ago, Tullius said:

It depends on your teacher. My brother once produced nitrocellulose in school. So it can't be that dangerous.

Even though it was under the supervision of teachers that produced themself nitroglycerine (the more dangerous brother of nitrocellulose) to put it into tiny tubes. And we students were allowed to hold those into a flame. Suffice to say that wearing safety goggles was essential, since even though they were only tiny droplets of nitroglycerine, you could feel the glass fragments on your skin from 1 meter away.

So it depends on how much your teacher trusts you and how well your school is equipped (my school was very well equipped).

Hmmm...it *can be* that dangerous.

"[Person] once did [thing] and didnt get maimed therefore it cant be that dangerous." is extremely spurious logic, especially when 2 separate people - at least one of whom is a chemist - have urged extreme caution.

Spoiler

Other things which are not true:

"We did an experiment with a tiny amount of [substance] therefore a large amount should be just as safe."

"The properties of a large amount of [substance] will be the same as a tiny amount of [substance]."

"If I can buy [substance] or buy the ingredients to make [substance] it must be safe."

You yourself say "even though they were only tiny droplets of nitroglycerine, you could feel the glass fragments on your skin from 1 meter away" - it would only take one student to neglect his safety goggles and you've got an eye injury here. I assume that the class experiment was carried out with proper safety procedures so that this would be very unlikely, however if ones aim is to experiment with rocket fuels, one is going to be working with far more than a tiny droplet.

Extreme caution and expert advice is necessary not because everything you do with these substances can cause death or injury, but because the line between safe and deadly is easily crossed and you dont always know that the threshhold has passed, otherwise there would never be any fuel/explosive related accidents.

Yes, there are some classroom experiments that involve these substances - I myself suggested encouraging teachers to do these experiments for the benefit of the OP -  but that does not in any way mean it is safe to start messing around with these things in your garage.

***

It is never appropriate to downplay the safety factors involved when working with this class of substance.

You can work with these things, but if you ignore advice and remove a finger or set fire to yourself, its on you.

***

I hesitate to post the below link because it is from an internet forum for amateur experiments with energetic materials and I dont want to encourage people to start copying down instructions and launching themselves into it thinking because someone says they are an expert on the internet then simply following some written instructions will replace the need for experience, professional advice and other safety precautions.

He was working with a far more dangerous substance than nitrocellulose, however, he felt that he had the necessary experience [with a certain amount of justification] to do this safely. And it still got away from him and he was hurt.

IF YOU TAKE THIS EXAMPLE TO MEAN THAT IT IS OK TO DO WHAT YOU WANT WITH NITROCELLULOSE BECAUSE THAT IS NOT WHAT WAS INVOLVED HERE, I CANNOT DO ANYTHING FURTHER TO HELP YOU

Spoiler

I post this link because the person:

A) regarded himself as an expert

B) was at least expert enough to have a certain amount of experience and own certain specialised equipment

C) was working with very small amounts

D) still suffered a serious incident that could very easily have ended much, much worse.

http://www.sciencemadness.org/talk/viewthread.php?tid=16612

 

 

 

 

 

Edited November 21, 2016 by p1t1o

[Green Baron]

"A lot helps a lot"

"Nothing comes from nothing"

"What's gone, is gone"

Valid in experimental chemistry as well as in the kitchen :-)

 

[Tullius]

34 minutes ago, p1t1o said:

**EDIT**

I'll just leave this here: http://www.mirror.co.uk/news/world-news/student-killed-another-injured-after-7693421

***********

Hmmm...it *can be* that dangerous.

"[Person] once did [thing] and didnt get maimed therefore it cant be that dangerous." is extremely spurious logic, especially when 2 separate people - at least one of whom is a chemist - have urged extreme caution.

  Hide contents

Other things which are not true:

"We did an experiment with a tiny amount of [substance] therefore a large amount should be just as safe."

"The properties of a large amount of [substance] will be the same as a tiny amount of [substance]."

"If I can buy [substance] or buy the ingredients to make [substance] it must be safe."

You yourself say "even though they were only tiny droplets of nitroglycerine, you could feel the glass fragments on your skin from 1 meter away" - it would only take one student to neglect his safety goggles and you've got an eye injury here. I assume that the class experiment was carried out with proper safety procedures so that this would be very unlikely, however if ones aim is to experiment with rocket fuels, one is going to be working with far more than a tiny droplet.

Extreme caution and expert advice is necessary not because everything you do with these substances can cause death or injury, but because the line between safe and deadly is easily crossed and you dont always know that the threshhold has passed, otherwise there would never be any fuel/explosive related accidents.

Yes, there are some classroom experiments that involve these substances - I myself suggested encouraging teachers to do these experiments for the benefit of the OP -  but that does not in any way mean it is safe to start messing around with these things in your garage.

  Hide contents

 

These experiments where done in classroom with the teacher present. Even though nitrocellulose was done as an project in an optional course, it was done in class (so even though the teacher wasn't overlooking the experiment permanently, he was close by).

I am from Luxembourg and don't know how these kind of projects is done in the US (where I guess TheEpicSquared is from). If this kind of stuff is not done in class: Don't even dream of doing it!

[TheEpicSquared]

24 minutes ago, Tullius said:

These experiments where done in classroom with the teacher present. Even though nitrocellulose was done as an project in an optional course, it was done in class (so even though the teacher wasn't overlooking the experiment permanently, he was close by).

I am from Luxembourg and don't know how these kind of projects is done in the US (where I guess TheEpicSquared is from). If this kind of stuff is not done in class: Don't even dream of doing it!

Well, thanks for the advice everyone (@Tullius I'm from Sweden by the way - we've been reading up on Swedish rocket laws - extremely strict ) but remember, we're using celluloid, not nitrocellulose. And we're using it in extremely tiny amounts (about the amount that can fit in a pen - although we won't use a pen as the fuselage) under close supervision of a teacher. We're also asking for permission from our local government, and we've decided to do a static fire before the actual launch, to make sure nothing goes wrong. Again, thanks for the advice - and don't worry, we'll be very careful.  

Edited November 21, 2016 by TheEpicSquared
accidentally used the swedish word :P

[p1t1o]

19 minutes ago, Tullius said:

These experiments where done in classroom with the teacher present. Even though nitrocellulose was done as an project in an optional course, it was done in class (so even though the teacher wasn't overlooking the experiment permanently, he was close by).

I am from Luxembourg and don't know how these kind of projects is done in the US (where I guess TheEpicSquared is from). If this kind of stuff is not done in class: Don't even dream of doing it!

From the UK here, we do have things like that in our classrooms, and with the appropriate supervision and equipment, many things can be demonstrated safely.

The concern here is people doing things under their own supervision, making assumptions about things for which they have little practical experience, which can get out of hand very quickly and when you least expect it. The thing about energetic materials is that they do not always behave in the manner you expect - this is demonstrably true even for those with the appropriate experience, which is why it is always the right choice to be finicky about safety.

And when you add in the interest in rocket motors, you start talking about quantities that could do some real damage.

This is not to discourage anyone from having a practical interest in rocketry - only to stress the need to go about it properly, which takes time and effort unfortunately.

 

1 minute ago, TheEpicSquared said:

Well, thanks for the advice everyone (@Tullius I'm from Sweden by the way - we've been reading up on Swedish rocket laws - extremely strict ) but remember, we're using celluloid, not nitrocellulose. And we're using it in extremely tiny amounts (about the amount that can fit in a pen - although we won't use a pen as the fuselage) under close supervision of a teacher. We're also asking for permission from our local government, and we've decided to do a static fire before the actual launch, to make sure nothing goes wrong. Again, thanks for the advice - and don't worry, we'll be very careful.  

Sounds like you've got your head screwed on ok - teacher supervision, legal permissions, Im assuming some level of appropriate lab equipment etc.   At first it sounded like you were going to be packing motors at home on your own!

Just treat celluloid with the same respect as you would any other flammable/explosive substance, Im sure you realise that a pen-sized amount may not level your school but it will have no problem causing permanent harm. Sometimes incidents occur because other, more dangerous substances can be formed in situ. 

The only reason, after all, that you are considering it as a rocket fuel is that it contains enough energy, and that energy is readily released.

You know the difference between a rocket motor and a bomb? The hole in the end.

Consider that one can make a decent bang with a pen-sized amount of normal baking flour. This was one of the demonstrations we did in my school

***

If anyone gives you stick for being paranoid, or mocks obsession with safety, this is a sign that they dont know what they are doing and you should start building distance!

Energetic materials is where chemistry and engineering become seriously adult.

There are old rocket scientists.

There are bold rocket scientists.

There are no old, bold rocket scientists.

***

Happy Launching!

 

[Tullius]

5 minutes ago, TheEpicSquared said:

Well, thanks for the advice everyone (@Tullius I'm from Sweden by the way - we've been reading up on Swedish rocket laws - extremely strict ) but remember, we're using celluloid, not nitrocellulose. And we're using it in extremely tiny amounts (about the amount that can fit in a pen - although we won't use a pen as the fuselage) under close supervision of a teacher. We're also asking for permission from our local government, and we've decided to do a static fire before the actual launch, to make sure nothing goes wrong. Again, thanks for the advice - and don't worry, we'll be very careful.  

I thought you were asking of what project would be possible as student project. If its ok for your teacher, it should be reasonably safe.

Yeah, i can imagine how hard it is getting permission to send something 100m up. But your science teacher should have some experience dealing with these kinds of problems. I remember when I was in school: How do we deal with the problems of buying certain chemical substances? Have stocks sufficient for decades of teaching in the basement, before it gets even harder. How to get examples of radioactive substances? Buy 100 year stuff from ebay and hope the post doesn't catch you.

[p1t1o]

1 minute ago, Tullius said:

Have stocks sufficient for decades of teaching in the basement, before it gets even harder. How to get examples of radioactive substances? Buy 100 year stuff from ebay and hope the post doesn't catch you.

O ma Gawd! XD

[0111narwhalz]

Can the normal vector be anywhere but the horizon?

Orbital physics, of course.