A helium balloon floats...it is lighter then air and a vacuum is lighter then He - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: April 30, 2019, 12:13:25 am
content: A balloon full of helium floats because it is lighter then air, another way of thinking of buoyancy is density; the density of the balloon is less then air, so what if you took another balloon and blew it up, froze the rubber in its shape and then sucked the air out making it lighter then the he balloon. Would this float? While it would be less dense then air it wouldn't be buoyant like helium balloons are? This also makes me wonder would a he balloon in a free falling box float?

author: apis
author_rank: Super Contributor
timestamp: April 30, 2019, 12:27:56 am
content: Yes, it would float just like a helium/hydrogen balloon. The reason you don't see anyone doing it is that the air pressure would easily crush any such "frozen balloon" unless you made it out of thick steel or concrete, but that would be pretty unwieldy (hmm, I wonder if it would be feasible if you made it large enough though...). Air pressure at sea level is about 100 kilo pascal i.e. about the equivalent of 10 000 kg per square meter (or 15 pound per square inch).With a helium balloon the pressure inside and outside the balloon is equal so it can be made of a soft material like rubber.In a free falling box everything floats!What happens if you try to pump out the air of a railroad tank car:

author: 0culus
author_rank: Super Contributor
timestamp: April 30, 2019, 12:47:07 am
content: I mean, even large cathode-ray tubes don't float, so it would have to be *really* big.

author: IanB
author_rank: Super Contributor
timestamp: April 30, 2019, 12:47:26 am
content: Quote from: Beamin on April 30, 2019, 12:13:25 amIf you took a heavy steel box, filled the middle up with air, and placed it on the sea, would it float? Steel is much denser than water and steel sinks, so what would happen?

author: apis
author_rank: Super Contributor
timestamp: April 30, 2019, 01:08:17 am
content: Buoyancy can be pretty counter intuitive to think about:(Annotation have been removed by Youtube but there are links to the solution in the description of the video.)Related: (lead helium balloon)

author: IanB
author_rank: Super Contributor
timestamp: April 30, 2019, 01:53:19 am
content: Quote from: apis on April 30, 2019, 01:08:17 amYay! I got it right. Apparently my reasoning ability is at least someone sound

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 30, 2019, 02:09:28 am
content: It was at one time proposed to use beryllium spheres (actual ones, not movie props) to hold vacuum. The metal shell is much heavier than, say, a rubber balloon, but perhaps the weight can be made low enough that it balances out?Turns out, nope, it's just not quite good enough. Not only do you need a very uniform sphere, but no matter how uniform it is, it still needs to be braced against unbalanced external forces -- bumps and bends from mounting and handling. It only takes a little imbalance to do what happened to the tank car! So you'd need a sphere that's wrapped in trusses to keep it supported, and the actual spherical walls would really be more like foil windows inbetween those supports. It might look like a buckyball instead.Beryllium would be the most likely candidate, for its extraordinary stiffness and strength to weight ratio. Some ferrous or titanous superalloys, or carbon fiber composite, might have superior strength to weight, but nowhere near the same stiffness. The stiffness is only superseded by heavier alloys (molybdenum, tungsten carbide..), which are inferior in strength/weight, or far too brittle (even moreso than beryllium itself) to fabricate.Maybe nowadays with slightly accessible metal 3D printing, it might be possible to revisit, and get comparable performance to traditional materials. But, suffice it to say: it's damn hard to beat having a gas that provides the same internal pressure, at a fraction of the weight, of the atmosphere outside it!Tim

author: Stray Electron
author_rank: Super Contributor
timestamp: April 30, 2019, 02:30:49 am
content: Quote from: 0culus on April 30, 2019, 12:47:07 amNot necessarily "really big" but really light for the volume that it occupies. Having adensity(weight divided by volume) less than than air is what makes a hydrogen or helium balloon float.In theory; a frozen, evacuated, rubber balloon would float but it would be impossible to make one.

author: 0culus
author_rank: Super Contributor
timestamp: April 30, 2019, 02:35:36 am
content: Of course. I was just proffering an example of an everyday (well, only for people who collect old TVs anymore) object with a vacuum in it that is strong enough to support itself against the atmosphere. Pretty sure, as you say with the frozen balloon example, you'd need some kind of ultra featherweight but super strong unobtainium to build a viable vacuum balloon.

author: rfeecs
author_rank: Frequent Contributor
timestamp: April 30, 2019, 02:48:29 am
content: There was a metal skinned airship, the "tin blimp" ZMC-2 (Zeppelin Metal Clad):https://en.wikipedia.org/wiki/ZMC-2But it wasn't ahttps://en.wikipedia.org/wiki/Vacuum_airship.Neal Stephenson's (fictional) book "The Diamond Age" featured vacuum airships:https://en.wikipedia.org/wiki/The_Diamond_Age

author: apis
author_rank: Super Contributor
timestamp: April 30, 2019, 02:58:11 am
content: The thing is, the internal volume of a sphere is proportional to the radius cubed, while the surface area is only proportional to the radius squared. If you can increase the size of the sphere without having to increase the thickness of the shell too much, at some point you will make the total sphere density less than air no matter what material you used in the shell. It's actually the same reason you can make helium balloons lighter than air. To get the shell strong enough and as light as possible, as Tim said, a buckyball is probably the way to do it, if at all possible. No doubt a helium/etc balloon is cheaper so there is no point, but in theory my guess is that it would be possible.Actually, now that I think about it I believe Bucky even proposed floating (air filled) buckyball cities at one time:https://en.wikipedia.org/wiki/Cloud_Nine_(tensegrity_sphere)

author: David Hess
author_rank: Super Contributor
timestamp: April 30, 2019, 03:17:17 am
content: Quote from: apis on April 30, 2019, 12:27:56 amThis is also why hot air balloons, blimps, and dirigibles are surprisingly difficult to shoot down. The pressure difference between the inside and outside is very low so any holes do not leak very much.

author: soldar
author_rank: Super Contributor
timestamp: April 30, 2019, 08:31:26 am
content: Quote from: IanB on April 30, 2019, 12:47:26 amThis is easier than it may seem at first because, being in the atmosphere it would fill with air naturally. I believe they already make something like this. They call it a "ship" if I am not mistaken.

author: MarkR42
author_rank: Regular Contributor
timestamp: April 30, 2019, 10:30:21 am
content: Maybe there is some lightweight uncrushable material (aerogel? micro-structured matrix of some kind?) which can be used to construct a sphere (with a thin shell to keep the air out) which could be buoyant by being evacuated.It sounds plausible but needs someone who understands the maths to do the sums.

author: soldar
author_rank: Super Contributor
timestamp: April 30, 2019, 10:45:17 am
content: Does not sound plausible at all. The least pressure difference will create forces which will distort and collapse the thing. An spherical cow is more plausible.

author: Stray Electron
author_rank: Super Contributor
timestamp: April 30, 2019, 11:48:58 am
content: Quote from: apis on April 30, 2019, 02:58:11 amThe problem with very large balloons and rigid airships is that they're unmanageable in even the lightest wind and even day time solar heating has a drastic effect on them. Go read the history of the USS Akron. Attempts have been made in recent decades to once again use lighter than air ships and to use modern technology such as weather radar, radios to avoid bad weather and computers to control the weight and balance and to control lift but none of them have been successful enough to justify them economically.

author: apis
author_rank: Super Contributor
timestamp: April 30, 2019, 12:58:26 pm
content: Never claimed it would be practical!Aeroscraft is a recent airship being developed in the US, (video shows a of a small scale proof of concept model). There haven't been much news about it the last couple of years though. They claim the main problem with cargo airships was that they required ballast and a large ground crew. This ship is supposed to have internal He compressors so that they can change the buoyancy during flight. (I hope they are better at building airships than making videos).Another interesting balloon, this one is from the 60s:https://www.nasa.gov/sites/default/files/thumbnails/image/5277461725_34624f8a73_o.jpg

author: Beamin
author_rank: Super Contributor
timestamp: April 30, 2019, 01:43:26 pm
content: Quote from: apis on April 30, 2019, 01:08:17 amA better question why do all three of the videos have the exact same number of views and likes and dislikes? I want to know how smart people are. Sometimes the group psychology of the comments is more interesting then the video. Why don't dislikes count? Ever taken the same comment and put it in multiple videos to see what happens? Or make a comment that you know will get 1k likes get bumped to the top, then a week later edit the comment to say something really unpopular and it looks like 1k people all agree with what ever you wrote. More mysteries for my restless mind. I'm a pathological thinker addicted to new thoughts. Remember before the internet you had to actually travel to the library to find knowledge and if they didn't have the book you would have to wait a week? Such barbaric and primitive times. I always thought the internet would make a generation of jeopardy players but instead we have trump. We are so screwed.I also worry we are going to run out of helium right as we find new uses for it as coolant for new technology and we won't have it because helium is too rare.

author: paulca
author_rank: Super Contributor
timestamp: April 30, 2019, 01:52:10 pm
content: Quote from: Beamin on April 30, 2019, 01:43:26 pmThis is how Facebook like farms work. They create non-sense but loveable inspirational quotes, fake competitions to win an iPhone or impostor pages pretending to be Disney or Land Rover and when they get a few 10s of thousands of likes they switch the page to what they really wanted to advertise. Or, more likely, they sell the page to someone else to advertise on.When I chastise my friends for liking and sharing scams they say things like, "But what is the harm?", the harm is that once well liked, shared and popular the page then switches over to being a scam conning old people out of their pensions or something similar, all help along by my friends. Bait, switch and scam.

author: Beamin
author_rank: Super Contributor
timestamp: April 30, 2019, 01:59:33 pm
content: Quote from: paulca on April 30, 2019, 01:52:10 pmFacebook is cancer on the internet and its metastasizing. Why would you give away all your privacy? You can't get it back.

author: apis
author_rank: Super Contributor
timestamp: April 30, 2019, 02:17:51 pm
content: Quote from: Beamin on April 30, 2019, 01:43:26 pmMe too. I thought it was the dawn of the information age! Turns out it was the dawn of the disinformation age.Quote from: paulca on April 30, 2019, 01:52:10 pmThat appears to be the case. The owners of the botnets and fake accounts aren't political, they just sell their services to the highest bidder.

author: paulca
author_rank: Super Contributor
timestamp: April 30, 2019, 03:39:45 pm
content: Quote from: Beamin on April 30, 2019, 01:59:33 pmTrust me that is not the main threat caused by Facebook or social media generally. It's much much worse than that.

author: rstofer
author_rank: Super Contributor
timestamp: April 30, 2019, 04:17:03 pm
content: Quote from: IanB on April 30, 2019, 12:47:26 amIt would probably violate the "Rules of the Road" and run into a container ship.

author: m98
author_rank: Frequent Contributor
timestamp: April 30, 2019, 07:14:52 pm
content: The idea of vacuum airships isn't new. It also isn't physically impossible, but it would require a unique structure and material to work. After all, its just a vacuum chamber that has to be lighter than the volume of air it displaces.

author: Bud
author_rank: Super Contributor
timestamp: April 30, 2019, 08:29:55 pm
content: Another silly topic opened by Beamin

author: Gyro
author_rank: Super Contributor
timestamp: April 30, 2019, 09:37:48 pm
content: Quote from: 0culus on April 30, 2019, 12:47:07 amI remember reading that the overall pressure on a 12" CRT is something like 13 Tons.

author: Rick Law
author_rank: Super Contributor
timestamp: April 30, 2019, 09:47:13 pm
content: A very interesting thing to try :A free floating helium balloon in the middle of the car with all windows closed, and the brake is applied to stop the car quickly. Where would that balloon go?(best if someone else is driving and the observer is alert and ready to prevent the balloon from obstructing the driver)

author: 0culus
author_rank: Super Contributor
timestamp: April 30, 2019, 10:08:17 pm
content: Quote from: Gyro on April 30, 2019, 09:37:48 pmSeems about right. CRT implosions areviolentand even though it's not technically an explosion at all, it will still get glass absolutely everywhere.

author: Stray Electron
author_rank: Super Contributor
timestamp: April 30, 2019, 10:39:49 pm
content: FWIW My pop used to work in a large TV shop in the early 1960s and they replaced a lot of TV CRTs. They took them to a pit that they had out back and would throw a large piece of steel at them. When they broke the CRT they would explode and throw heavy thick pieces of glass 15 feet or more in every direction. I worked in a TV shop about 15 years later and we destroyed CRTs by breaking the small glass tit on the very back of the neck. We used any kind of metal like a large screw driver and just "chopped" the tit off and air would rush into the CRT for several seconds and then stop and none of the rest of the CRT would break or explode. Yes, I know it's not actually an explosion since the CRTS are filled with a vacuum and not pressure but it certainly looked like one.

author: apis
author_rank: Super Contributor
timestamp: April 30, 2019, 11:44:40 pm
content: Quote from: Gyro on April 30, 2019, 09:37:48 pmAt sea level with the equivalent of 10 ton per m2it would correspond to a surface area of the CRT of 13/10 = 1.3 m2, sounds about right.

author: amyk
author_rank: Super Contributor
timestamp: May 01, 2019, 01:24:10 am
content: Exercise for the reader: What compressive strength and other properties would a material have in order for it to be able to create a buoyant vacuum balloon?Quote from: Stray Electron on April 30, 2019, 10:39:49 pmThere's a term for that, the "opposite of an explosion" is animplosion.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 01, 2019, 03:22:16 am
content: Quote from: Beamin on April 30, 2019, 01:43:26 pmThey don't. YT glitch for you?Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 01, 2019, 03:24:02 am
content: Quote from: Rick Law on April 30, 2019, 09:47:13 pmI already know the answer to this as my car's cabin air is highly stratified in wintertime. That is to say, the hot air rises to the roof and the cold air stays at my feet.When taking off, the air suddenly gets pleasantly warm in the front seats. Why is that?Tim

author: raptor1956
author_rank: Frequent Contributor
timestamp: May 01, 2019, 04:31:34 am
content: Quote from: Rick Law on April 30, 2019, 09:47:13 pmThe air density will be higher towards the front of the car because the acceleration will do that. The He balloon will then move backwards in the opposite direction. Gravity is indistinguishable from acceleration and, according to general relativity, gravity and acceleration are the same thing. So, if an He balloon moves up against the accelerating force of gravity then it will move backwards against the accelerating force of braking!Brian

author: james_s
author_rank: Super Contributor
timestamp: May 01, 2019, 06:31:59 am
content: Quote from: 0culus on April 30, 2019, 10:08:17 pmWell it's easy to calculate, ~14.7 pounds on every square inch, so add up the number of square inches of the entire surfae area of the CRT, it's substantial.It starts out as an implosion, but the bits of glass don't stop when they get to the middle, they pass by one another and for all practical purposes it becomes an explosion. About 20 years ago I was disposing of a badly worn out 19" CRT from an arcade monitor and I forgot to crack the pip off the neck before I threw it away. I heaved it toward the dumpster but saw it was coming down a little short and spun around just as I saw the bell of the tube contacting the hinge on the lid. There was a deafening BOOM as glass sprayed around about a 15' radius from where I was standing. I stood there in shock for a moment as I checked to see if I was injured and somehow I escaped unscathed. My hands were shaking for a good 20 minutes after that though and my left ear was ringing for quite some time.I remember hearing a similar story from an old TV tech who *twice* tried flipping the mounting ears around by removing the implosion protection band holding them from around the circumference of a tube and the tube imploded in the process. He also walked away unscathed both times, not knowing how. CRTs are pretty amazing devices, an incredible amount of engineering went into getting them to where they were at their peak. Sadly they are vanishing very quickly and much of that knowledge will be lost.

author: Gyro
author_rank: Super Contributor
timestamp: May 01, 2019, 11:50:26 am
content: Quote from: james_s on May 01, 2019, 06:31:59 amThat was a lucky escape.My favourite (and possibly safest?) method was to run a fine pcb drill through the middle of the metal EHT contact on the bell of the tube. It really would hiss for quite a long time, especially if you left the drill in.I always though it was a waste of useful reservoir of hard vacuum. If you kept the system volume very small and were quick with a pipe and bung arrangement, you could probably use it for some physics experiments, a low pressure discharge tube for instance. Certainly sticking a damp finger over the contact gave a good impression of what it would feel like to be being exposed the the vacuum of space.

author: james_s
author_rank: Super Contributor
timestamp: May 01, 2019, 03:26:16 pm
content: Once even a bit of air hisses in it's not really a very good vacuum anymore, no better than can be achieved with a cheap mechanical vacuum pump. The difference between the vacuum you can pull with something like a repurposed refrigeration compressor and the hard vacuum in a CRT is very little in terms of mechanical forces. It's a huge number of gas molecules but we're talking a few thousandths of an atmosphere of pressure. It's not gonna feel any different to stick your finger into outer space than to stick it into a vacuum chamber connected to a cheap mechanical pump here on earth. If you're trying to make a vacuum tube it makes a big difference though, the residual gas has to be removed.

author: Beamin
author_rank: Super Contributor
timestamp: May 01, 2019, 04:25:14 pm
content: Quote from: Bud on April 30, 2019, 08:29:55 pmIf I didn't have silly topics what would I have? Some of these silly topics have answered long running questions that can't just be typed into google. Like how does the dust form in space? Through a few of the posts the answer could be deduced: electrostatic attraction brings the dust together where UV light ionizes it to make chemistry happen without liquid(solutions) and pressure and heat. Most people just said "gravity" but if you think about it that was wrong and gravity is too weak to clump little sand grains together. The dust in the universe is the consistency of cigarette smoke and the dense gas clouds are still less dense then our best vacuums here on earth.Also the side discussions lead me to think of new things I would have never considered, or bring obscure aspects to light on the topic. Being intelligent is lonely I realized that at a young age so if you have a whole group of intelligent people it is wise to use that rare opportunity to pick their brains. Imagine the conversations that went on at Los Alamos? Or we could talk about sports, TV shows, or what ever drivel normal people talk about around the water cooler.

author: German_EE
author_rank: Super Contributor
timestamp: May 01, 2019, 05:24:19 pm
content: A helium balloon occupies a volume ofVcm3. It floats upwards becauseVcm3of air weighs more than the balloon and the helium.If you want a container containing a vacuum to float upwards then it must meet the same condition. It must weigh less than the equivalent volume of air and this is a BIG challenge because of the wall thickness required to stop the container from imploding inwards.I do not think that this is possible but I am willing to be proved wrong.

author: IanB
author_rank: Super Contributor
timestamp: May 01, 2019, 06:28:43 pm
content: Quote from: Beamin on May 01, 2019, 04:25:14 pmIf this is true, how did the first stars form? The first stars formed only from hydrogen, which is the least dense substance known, and which is spread out very thinly in space. And yet, hydrogen was compressed into balls so dense and hot that nuclear fusion started. If not gravity, then what?

author: apis
author_rank: Super Contributor
timestamp: May 01, 2019, 06:57:54 pm
content: Quote from: Gyro on May 01, 2019, 11:50:26 amInterestingly it's not the vacuum that is making the impression, it's the pressure of the atmosphere you feel (or the pressure differential really). If you are suddenly exposed to the vacuum of space nothing super dramatic happens. It is still bad, because you would suffocate and at low pressures water boils at body temperature, etc.But you wouldn't blow up.

author: Vtile
author_rank: Super Contributor
timestamp: May 01, 2019, 07:07:26 pm
content: Quote from: IanB on May 01, 2019, 06:28:43 pmEther vortexes you silly.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 01, 2019, 07:30:25 pm
content: Quote from: Beamin on May 01, 2019, 04:25:14 pmThat seems to be a common experience for a lot of young engineers in (elementary to middle) school - hard to find friends. Smart girls have the additional problem of mean guys who can't accept the idea of a girl being smarter than them.

author: apis
author_rank: Super Contributor
timestamp: May 01, 2019, 09:04:40 pm
content: Quote from: amyk on May 01, 2019, 01:24:10 amI give up. Some insights can be found here though:http://eprints.keele.ac.uk/1563/1/Stability.pdfQuoteSo the buckling pressure decrease withR2(makes sense, since the curvature decrease when R increase and a dome is stronger than a flat sheet), it has to be countered by making the shell wall proportionally thicker, which is bad news.But rather than a solid homogenous shell I would imagine you would use a some kind of space frame truss with only a thin sheet preventing air from entering, or a sandwich composite material, or both. Not so easy to calculate exactly what it would take.

author: Beamin
author_rank: Super Contributor
timestamp: May 01, 2019, 11:10:02 pm
content: Quote from: IanB on May 01, 2019, 06:28:43 pmElectrostatic attraction apparently. The universe was also much denser. Gravity across an atoms size is pretty weak. The first gas clouds would need to be shocked into forming stars like when supernovas compress gas clouds. The universe's non uniformity might cause these waves to form. Not much info on what the universe was like on a practicality level when it went from orange hot to stars around 380ka old after reionization. Why is it _re_ionization? If its re that's the second time, when was the first? Astronomers and Neil deGrasse Tyson will never tell you this.If you had a sheet of graphene held apart by nano tubes on the outside into some type of fram work would work, problem is how do you make it?

author: james_s
author_rank: Super Contributor
timestamp: May 01, 2019, 11:29:58 pm
content: Quote from: apis on May 01, 2019, 06:57:54 pmGiven how painful it is (for me anyway) in my sinuses and ears when the pressure changes even just taking off and landing in an airliner which is pressurized so not even a huge pressure change, I would imagine that suddenly stepping into the vacuum of space would feel pretty darn dramatic even if my body didn't blow up. I would bet all that atmospheric pressure in various bodily cavities would not feel very good at all.

author: Rick Law
author_rank: Super Contributor
timestamp: May 02, 2019, 12:14:21 am
content: Quote from: raptor1956 on May 01, 2019, 04:31:34 amYup - it is really fun to watch / play with. Very counter-intuitive to have everything come flying towards the front while the He balloon rush to the back.As said before - best done when someone else is driving and ensure nothing will obstruct the driver - else it could be danagerous. Do this at your own risk.

author: apis
author_rank: Super Contributor
timestamp: May 02, 2019, 12:24:10 am
content: Quote from: james_s on May 01, 2019, 11:29:58 pmYeah, and how big a change in pressure you experience and how quickly you decompress probably has a large effect as well. Astronauts doing EVA have lower pressures than what we have a sea level, some as low as 20.7 kPa (3.0 psi), they use a pure oxygen atmosphere inside the spacesuits to make sure you get enough oxygen. The sea level pressure is about 101.3 kPa (14.7 psi). The ISS apparently use sea level pressure and a roughly standard atmosphere though. But most movies/tv-shows depict it overly dramatic.

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 02, 2019, 02:12:44 am
content: I always kinda wondered about that too, but I guess the issue with a vacuum is the practicality of it. You need a very thick/strong chamber and the material will end up being too heavy for it to be practical.

author: hamster_nz
author_rank: Super Contributor
timestamp: May 02, 2019, 02:29:28 am
content: I am surprised that nobody has looked at this the other other way... trying to build a 1m^3 vacuum balloon is like building something that holds a cubic meter of air at atmospheric pressure, weighs less than 1.2 kg (the weight of 1m^3 of air), and can be submerged to 10 meters in water without crushing.At 10 meters the water pressure is about 1 bar.Likewise silly question. Does a jar with a lid on it weigh more when it is in a vacuum?

author: IanB
author_rank: Super Contributor
timestamp: May 02, 2019, 02:44:57 am
content: If you work out how much all the air in a typical room weighs, the answer is surprising.

author: Beamin
author_rank: Super Contributor
timestamp: May 03, 2019, 05:35:36 pm
content: Quote from: IanB on May 02, 2019, 02:44:57 ampv=nRT = a lot. When they make precision weights they have to account for the volume and the air pressure it takes up.