I find science confusing and with the things you can do with photoshop I don’t know what to believe or not. Can you really float a boat like this in mid air? Or is it just a trick? Also the voices seem faked.
Thanks
Welocme to the SDMB. 
First, it’s not a boat, it’s some aluminium foil!
Helium is lighter than air, which is why balloons filled with helium float upwards. Since aluminium foil is pretty light too, there’s no reason it won’t float.
I have a helium balloon with a radio receiver and a twin fan motors attached. The helium has enough upthrust to lift everything, and you can steer the balloon by using either or both of the fans. 
Absolutely possible.
Yea sure I understand the heluim but what about the other stuff is it really sooo heavy that air floats on it??? How is that possible?
Forgive me if I’m misunderstanding you, but they’re floating it not on the helium, but the sulphur hexafluoride, which is heavier than air. Otherwise, the helium would have escaped the tank. As it is, the sulphur hexafluoride (which is 5 times as dense as air), is contained in the fish tank, and is dense enough to support the weight of aluminum foil
It’s all about density. The Sulfer Hexaflouride is denser than air, so it’s contained in the aquarium and can’t roll out of it. Think of it as the opposite of Helium.
As for the voices… never did whippits, huh? 
Absolutely real. Sulfur hexafuoride can be thought of as the “opposite” of helium in some ways, which the girls illustrate in their video. It’s denser than room air, where helium is lighter than room air. It makes your voice deeper, instead of higher, and it pushes things down instead of lifting them up! It’s really cool stuff to play with, and it’s pretty safe.
Rosie and Anna have a website with other fun videos, too. Some science, some crafts; it’s pretty neat!
You’re quite correct.
I wasn’t sure how much science Scipro8 could take, so started with the helium, since that was mentioned and shown in the video first.
Sulfur hexafluoride has a density of about 0.006164 g / cc at atmospheric pressure and temperature.
A 1 square foot (300 mm) piece of aluminum foil, about 0.03mm thick, has a volume of 2.7 cc, so masses (density = 2.7) about 7.3 g
In order to float, that 7.3 grams would have to displace 1.18 liters of gas.
That’d require a boat about 12cm long, wide and tall.
That’s doable with a 30 X 30 cm piece of foil.
It can be safely handled, but it isn’t “safe”… it displaces atmosphere, and can pool in low areas and so poses the same hazards as other lab gases, such as nitrogen and carbon dioxide.
I’m always dubious of people who let anyone, especially kids, inhale stuff in labs. Far too easy to have a tragic accident. Also, it’s a total disregard for the basic lab safety that teachers are supposed to drum into kids. It’s one of the things that really annoys me about Mythbusters, especially when Adam takes Helium straight from the tank.
Not having a go at you. I’ve just been in labs where poor safety caused real injuries amongst people who should have known better.
And all that roughhousing was atrocious! They should at least have been wearing helmets ;).
I had the same reaction. Helium is safe enough to inhale, since it’ll escape from your lungs on its own quickly enough. But sulfur hexafluoride will just stay in your lungs, so you have to do a handstand afterwards to get rid of it. It can be done safely, but I wouldn’t let children do it.
Back on topic, it should be noted that any gas will gradually diffuse out of an open container, even if it is heavier than air. That’s why they had a cover over the bucket before they used it, and why there was a hose in the big fish tank (to continually replenish it).
Yeah, I think the lungs are a sufficiently turbulent system to be able to expel denser gases along with the air.
I’m just amazed that something called sulphur hexafluoride isn’t horribly toxic- it sounds like it ought to be.
Here is another great effect of sulfur hexafluoride.
Sulfur and fluorine are both toxic more or less because they both really like to react with things. Put them together, and they both take the opportunity to react to a very great degree, until they turn into something (SF[sub]6[/sub]) which is about as reacted as it can get. So it can’t react any more.
pulykamel, I won’t dispute that MD’s word. But I likewise won’t go huffing any SF[sub]6[/sub], if it’s all right with him.
And that’s why horribly reactive toxic sodium and horribly reactive toxic chlorine are edible when reacted together.
Personally, I’m scared of sodium chloride (both sound so dangerous: sodium! and chloride!), not to mention dihydrogen monoxide.
Just to get you feeling freaky again, Sulfur Hexafluoride is structurally (and other ways) similar to Uranium Hexafluoride, one of the stable uranium compounds that was used in, for instance, isotope separation. They used to run tests with SF6 to see how well procedures with UF6 would work.