# Helium Balloon Levitation

1. Jan 13, 2010

### skilet

I wonder if it is possible to make a helium ballloon to Levitate in the air without touching the ceiling?
Something like this.

Thanks,

Last edited by a moderator: Apr 24, 2017
2. Jan 14, 2010

### jmatejka

Neutral Buoyancy

3. Jan 14, 2010

### rcgldr

In the video, the balloon is being suspended by a stream of air, similar to this ping pong ball demo (the spinning is accomplished by angling the stream):

In the case of a helium balloon, as it rises into lower density, lower pressure air, it expands a bit, reducing it's density as well, allowing it to rise further, and expand more, until eventually, the balloon surface expands beyond it's elastic range, and becomes rigid enough to resist significant further expansion, keeping the internal density near constant, and the balloon will then hover at a specific altitude. Another method is to simply leave the balloon open at the bottom, so once it expands to full size, the expanding helium escapes out the bottom. For a relatively low ceiling, you'd need to use a precise ratio of air and helium in the balloon and fill it to a specific amount, and perhaps use some small amount of weight. Density change of the air is tiny over a small change in altitude.

Last edited by a moderator: Apr 24, 2017
4. Jan 14, 2010

### Danger

The trick to do it for real is indeed to achieve neutral buoyancy, which can be done with ballast which will have to be experimentally determined. In the case of the video, though, it's an illusion perpetrated by a professional's means. I know how it's done, but I'm not going to tell you because it would ruin the illusions of a few thousand 'magicians'. (I'll give you a hint, though; somewhere in this site is a thread started by me that references the technique involved. )
Good luck searching.

edit: Aww, you sneaked in on me, Jeff.
Come to think of it, that wasn't in a thread that I started; just one that I responded to. Anyhow, the post was about my Johnny Astro toy that I had as a kid.

5. Jan 14, 2010

### rcgldr

Considering how many levitating ping pong ball videos there are at youtube, plus store displays that levitate beach balls over household fans, I doubt it could be considered a secret. I decided to combine hovering, spinning, and "shooting" ping pong ball sequences in a one take video.

Last edited: Jan 14, 2010
6. Jan 14, 2010

### Danger

I wasn't putting you down on that, Jeff. I'm still a net 'newbie', so I didn't realize that it was currently common knowledge. Even with the Johnny Astro on the market when I was a kid, it absolutely astounded people. I could make it take off, fly around, hover... and it even had a little hook on the bottom to pick stuff up and bring it back to the landing pad. I've incorporated parts of that old sucker into a couple of different projects and Hallowe'en costumes over the past 40 years or so.
Here's a link to the toy itself:
http://johnnyastro.com/" [Broken]

Last edited by a moderator: May 4, 2017
7. Jan 14, 2010

### Yeti08

Yes, I have (accidentally) made helium balloons levitate a few times. It happened, I believe, for two reasons - the baloon had lost some helium having been filled a few days prior, and the balloon was still warming up having just been exposed to liquid nitrogen.

8. Jan 15, 2010

### nucleus

Must be a special balloon.

Helium balloons are used in the weather service for two purposes. First as radiosondes where it carries a radio transmitter aloft. The maximum altitude to which the balloon ascends is determined by the diameter and thickness of the balloon. Balloon sizes can range from 150 grams to 3000 grams. As the balloon ascends through the atmosphere, the pressure decreases, causing the balloon to expand. Eventually, the balloon will expand to the extent that its skin will break, terminating the ascent. An 800 gram balloon will burst at about 21 kilometres (69,000 ft).
Second as a ceiling balloon, where it measures the height of the cloud base.
http://en.wikipedia.org/wiki/Ceiling_balloon
Both of these balloons rise until they break.

9. Jan 15, 2010

### skilet

I heard that if you fill the balloon with 1/2 of helium and 1/2 air it will stay in the air instead of going all the way up. Will that work?

10. Jan 15, 2010

### diazona

As the previous posters have said, there is some ratio of helium to air that would make the balloon neutrally buoyant. Generally it wouldn't be 1/2 and 1/2, though.

In fact, at least approximately, you could calculate it. If $f_\text{He}$ is the fraction of helium in the balloon by mass, you'd need
$$mg + f_\text{He}\rho_\text{He}g V + (1 - f_\text{He})\rho_\text{air} g V = \rho_\text{air} g V$$
Weight on the left, buoyant force on the right.
$$mg + f_\text{He}(\rho_\text{He} - \rho_\text{air}) g V = 0$$
or
$$f_\text{He} = \frac{m}{V(\rho_\text{air} - \rho_\text{He})}$$
For a regular latex party balloon (mass 2g, volume 14L) I get about 14% helium. Obviously this number would vary for different kinds of balloons. And even if you did get the exact fraction of helium required for neutral buoyancy, in practice it would be a very delicate balance because a slight air current or any other force would be enough to start the balloon moving one way or another.

11. Jan 15, 2010

### rcgldr

I meant as one that could levitate, not a weather balloon. A better example of a near neutral balloons are model and full size blimps.

12. Jan 15, 2010

### Phrak

It's not a helium ballon. Watch closely. Pay attention! It's a common balloon full of air. (mutter, mutter, observational physics, mutter, mutter)

13. Jan 17, 2010

### Danger

Agreed, nor was the Johnny Astro. I should have specified that in my previous posts, but I was trying to work the possibility of ballasting a helium balloon without giving away the (apparently not so secret) method that was used in the video.