Talk:Soap bubble

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Former featured article Soap bubble is a former featured article. Please see the links under Article milestones below for its original nomination page (for older articles, check the nomination archive) and why it was removed.
Main Page trophy This article appeared on Wikipedia's Main Page as Today's featured article on April 12, 2004.
To-do list for Soap bubble: edit · history · watch · refresh
  • Somebody please change the 2nd column for reflection and interferences section. The red light should be 180 degrees out of phase instead of being in phase. The one ray on the outside of the bubble goes through hard reflection.
  • what are they made of?
  • Lead section is inadequate.
  • The "How to make soap bubbles" section, by its very nature, reads like a "how to", and does not fit in an encyclopædia.
  • There are only a small handful of references, none of which are in-line. From the names of the references given, it seems unlikely that they would cover all the subject material covered in the article. The references need to be more specific.
  • "See also" and "External links" sections contain descriptions of links in a very un-encyclopædic manner.
  • Several sections do not sit right as sections: for example "Coloured bubbles" and "Structure" are (almost) single paragraphs.
  • Mix of BrE and AmE.
  • The whole thing is quite poorly written: the English is not up to standard. Take for example the lead: "Soap bubbles usually last for only a few moments and then burst either on their own or on contact with another object." - there are no commas in this sentence, where they are required. This writing continues throughout.
  • The captions of the photos are poorly written and not informative.
  • The description of interference is still not quite correct. As far as I can tell as of 10/19/2006, the 180 degree phase shift in the wave reflected from the first interface (air to water) is not mentioned in the main article. This is mentioned in the discussion page, but I guess never made it to the article? There are drafts on the discussion page of improved figures, but these too are not quite correct. The 180 degree phase shift is a very important part of the effect!-Skoch3

he 'thin film' colouring phenomenon is called Newton's colours, I'm not sure about the history of it, link should be integrated into the paragraph, I tried but my writting didn't look good enough. I think Newton studied it first (hence the name ;), personally I don't know much about it, I rather read about simulations of the graphic effect.

Contents

[edit] Suggestions for improvements

"... I was told today that soap bubbles are permeable to carbon dioxide but not to air. Does anybody in this community know why/if this is so?"

Actually, my experience in this matter is a bit different. The air in a soap bubble does escape the bubble through the film and therefore, the bubble begins decreasing in size as soon as it is completed. If it were to "live" long enough, it would shrink back down to a small pool of liquid. The rate is so slow that it isn't readily noticable during the "life" of a normal bubble but if you keep it in a jar you might well notice this changing size. I saw 200 day old bubbles blown by a man (Eiffel G. Plasterer) and kept in that way. He told me that his oldest was 340 days old (it never popped, it shrunk down to liquid ... he told me that he once used a microscope to watch one continuing down within the liquid).

But, there is a difference with carbon dioxide which permeates the film so readily that it will readily diffuse INTO the bubble against the flow of air being pushed out by the internal pressure. I have filled a bathtub with carbon dioxide gas (I put dry ice in the tub and allowed it sublime off into the invisible gas without adding water to produce the familiar "fog" effect so loved by horror movie directors) and then blew bubbles which floated on the gas. But after a bit, the bubble slowly descends into the gas and can be seen to grow in size!

If you then try to lift the bubble out with the bubble wand, you'll readily see that it has become heavy with the gas and becomes difficult to lift (it droops into a drop shape).

I have one further to actually watch the invisible gas entering the bubble. This takes a bit of explaining:

I blew a grapefruit sized bubble and then blew a plum-sized smoke-filled bubble that was connected to it at the bottom. Waiting a bit to allow the spinning air inside to calm down, I then broke the wall that kept these two bubbles apart (I'm an entertainer who does a performance with soap bubbles ... I used a wet straw to go inside of the bubble and, touching the wall that separated the two, I sucked a bit thereby popping that wall without destroying the two bubbles but causing them to merge into a single larger bubble).

The smoke hangs low in the bottom of this new larger bubble. But when I put that bubble into the carbon dioxide gas, I was able to watch the gas enter the bubble creating clear lanes of air within the dense smoke. This eventually stirs up the smoke and it mixes more evenly throughout the bubble.

So, the film is permeable to both the air and to the carbon dioxide but one more readily reacts in that way.

I have written a book on soap bubbles that is now out of print and I perform regularly at science centers, universities, and elementary schools (as well as my regular nightclub and other show-biz gigs). Explaining the physics in a way that is accessible to people without a science background is not a simple matter. This article is wonderful.

Tom Noddy www.tomnoddy.com

The roof of the National Aquatic Centre in Beijing being built for the 2008 Olympics has three-dimensional strucure designed after soap bubbles. You can see images at http://www.arcspace.com/architects/ptw/ . It looks very cool -- and should be an efficient way to bear the loads of the roof.

Phil Earnhardt

[edit] Two potential problems

I think there are two errors in the article, but I don't want to change an article that's already been vetted for featured-article status without discussion.

  • Water droplets are drop-shaped because of air resistance (drag), not gravity. In free fall in a vacuum they would be spherical, whereas moving through air in the absence of gravity they would be drop-shaped. The same would be true for soap bubbles, except of course those wouldn't exist if there were no air. That they are almost spherical is due to the much lower terminal velocity at which they travel through the air, compared to water droplets. This of course has to do with their weight, but air resistance is the primary cause for the drop shape; gravity is only a secondary cause, being one way to set things in motion through air.
  • The article says that the interference comes about because the internally reflected ray travels longer. This explains only the changes in interference due to thickness; the "baseline" for these changes, the complete cancellation in the limit of vanishing thickness, is due to a 180° phase jump in the outer reflection.

Fpahl 00:26, 22 Sep 2004 (UTC)

  • You are completely right and should just be bold and edit the article. To be honest I'd forgotton about the phase shift when n1 < n2. I'll tell you what - you fix the article and i'll fix the diagrams. Theresa Knott (taketh no rest) 13:18, 22 Sep 2004 (UTC)
    • Now that's what I call division of labour :-). I'll do that. Fpahl 10:40, 23 Sep 2004 (UTC)
    • OK, I've done the gravity bit. I'll do the reflection bit tomorrow. I don't think the images need any changing, actually, since they only show phase relations for finite path length differences. The captions do, but I can do that together with the text. Speaking of the images, there's a little red squiggle underneath one of the '1's in the upper diagram. And I don't understand the meaning of the white and green circle connected by a line in the lower one. Fpahl 14:23, 25 Sep 2004 (UTC)
    • I've now changed the bit about interference. There was a further problem with it: The cancellation is due not just to two reflections, but to a whole series of them. I've tried to explain this without going into mathematical details. The image captions are now completely out of tune with the text, but I haven't changed them yet since Theresa is deciding whether to change the diagrams themselves. Fpahl 12:48, 1 Oct 2004 (UTC)
      • I'd suggest deleting them until they are fixed. They're confusing at the moment. Filiocht 12:55, 1 Oct 2004 (UTC)
        • I will definately amend the images this weekend come hell or high water. The problems you describe false articfacts created when I bodged the drawing :-( they will be easy to remove. Theresa Knott (The torn steak) 13:02, 1 Oct 2004 (UTC)
          • I finally fixed the two images. (you may need to refresh your cache in order to see it) I'm working on two more, one to show the phase relationships, one to show an infinite number of reflections.Theresa Knott (The torn steak) 20:00, 5 Oct 2004 (UTC)


Right here is the first diagram. I've ignored refraction effects to concentrate on the phases of the two reflected rays. I've also ignored all other reflections etc and only concentrated on the two we are actually interested in. Thoughts anyone?

Can you do them so that the sine waves are at zero amplitude at the reflection points? It might be a little clearer what's happening.
—wwoods 04:03, 6 Oct 2004 (UTC)
The wave is partically reflected at X and O. At X the wave suffers a 180° phase shift as it reflects off the air/water boundary. At O no such phase shift occurs at the water/air boundary. Nevertheless, since the part of the wave that is reflected at O has had to travel the depth of the film and back again, the difference in path length cancels out the phase shift, and the two parts of the wave emerge in phase.
The wave is partically reflected at X and O. At X the wave suffers a 180° phase shift as it reflects off the air/water boundary. At O no such phase shift occurs at the water/air boundary. Nevertheless, since the part of the wave that is reflected at O has had to travel the depth of the film and back again, the difference in path length cancels out the phase shift, and the two parts of the wave emerge in phase.
As the bubble gets thinner and thinner, the path difference between the two parts of the reflected wave (from the top and bottom of the water) get's less and less. When the thickness approaches zero, only the phase shift will matter and so the two parts of the wave will be 180° out of phase. This is true no matter what the wavelength.
As the bubble gets thinner and thinner, the path difference between the two parts of the reflected wave (from the top and bottom of the water) get's less and less. When the thickness approaches zero, only the phase shift will matter and so the two parts of the wave will be 180° out of phase. This is true no matter what the wavelength.

I fixed some typos and other small problems in the captions above. I'm in two minds about this use of only two rays. On the one hand, this might make it easier to understand the basic idea. On the other hand, it's really misleading. At shallow incidence, when the reflectivity is high, the second reflection is very insignificant compared to the first, and it's only the long train of later reflections that cancels the first. The images create the false impression that the second ray has the same amplitude as the first. Also, in the left-hand case, where the second reflection is in phase with the first, due to a path-length difference of 180°, the subsequent reflections alternate in phase. I'm aware that all this is very hard to explain in an image, but I don't want people to take away an oversimplified impression of there being cases where the interference is fully constructive or fully destructive.

In case it's of any help, here are the details of the mathematics. Denoting the factor by which the amplitude gets multiplied upon the exterior reflection by r, we have the following factors:

r for the exterior reflection
1 + r for transmission into the film
− r for each internal reflection
1 − r for transmission out of the film

Also we incur some phase factor Δ for each traversal of the film. Then we get the following series for the sum of the amplitudes of the transmitted rays:

(1 + r) \Delta (1 - r) + (1 + r) \Delta (-r) \Delta (-r) \Delta (1 - r) + \ldots

=(1 + r) (1 - r) \Delta (1 + (\Delta r)^2 + \ldots)

= (1 − r2)Δ / (1 − (Δr)2)

Taking the squared magnitude of this yields the total transmittance. The phase factor Δ doesn't change the magnitude, so with Γ = Δ2, the phase factor incurred by a double traversal of the film, and with R = r2, the reflectance of a single interface, we get the total transmittance

\left|\frac{1 - R}{1-R\Gamma}\right|^2

The total reflectance is just one minus this; it could also be obtained by summing the amplitude factors of the reflected rays:

r + (1 + r)\Delta(-r)\Delta(1 - r) + (1 + r)\Delta(-r)\Delta(-r)\Delta(-r)\Delta(1 - r) + \ldots

=r + (1 - r^2) (-r) \Gamma (1 + r^2\Gamma + \ldots)

= r − rΓ(1 − r2) / (1 − r2Γ)

Here the first r represents the exterior reflection, and the other term represents the sum of all subsequent reflections. Since the exterior reflection doesn't suffer the 1 − r2 attenuation from the two transmission processes (which is very significant at high reflectances), it forms a term by itself, whereas the second reflection contributes the first term in a geometric series whose sum at high reflectances is much larger than just the second reflection.

I hope that was sort of clear... Fpahl 03:10, 7 Oct 2004 (UTC)

[edit] Glue-based bubbles?

How do you call that organic solvant-based yellowish or brownish glue in English? There are some people who use this gue to blow large and durable bubbles. It's actually a dangerous glue that you don't want to inhale. Makers of that glue have to add mustard oil in it to stop kids from inhalation. -- Toytoy 08:31, Jan 1, 2005 (UTC)

[edit] New colored bubbles

I just read about an inventor using 10+ years inventing colored soap bubbles. They're schedualed for release Febuary 2006 called Zubbles (www.zubbles.com) The story I read: http://www.popsci.com/popsci/science/0a03b5108e097010vgnvcm1000004eecbccdrcrd.html

yah, already an entry at Zubbles. :) --Quiddity 19:16, 28 November 2005 (UTC)

[edit] color bubbles

i heard on NPR a few months ago about a guy who just invented solid color bubbles. he said they'd be for sale starting this summer or spring. how can i get more info? Kingturtle 02:14, 22 February 2006 (UTC)

Zubbles! :) --Quiddity 03:36, 22 February 2006 (UTC)

[edit] Fact change that doesn't seem right

[1] (Ignore the deletion of the bottom of the page this is a glitch in Wikipedia)

I reverted this edit because it was a fact changes that didn’t seem like it was true.

  1. One can make a bubble out of pure substances other than water
  2. The air pressure in the bubble can't decrees due to temperature because it was blown at that temperature and has noting to do with touching a surface. Maybe somebody should expand on that.

[edit] Guiness Records

Under this site you can find some informations about Guiness Records related with soap bubble. I suggest to expand this article about these records. Visor 12:13, 3 May 2006 (UTC)

[edit] Salt in bubble solution

One of the formulae given is

  • 100 g sugar
  • 2 to 3 tablespoons salt
  • 1.4 L water (distilled water is better)
  • 150 ml dish washing detergent
  • 12 ml glycerin

While most of the components are explaied earlier, there is no explanation why salt is an improvement.

(Going metric for the rest of the formulae would also be useful for the world outside the US.) --12:36, 24 June 2006 (UTC)

[edit] Fair use rationale for Image:Zubble.JPG

Image:Zubble.JPG is being used on this article. I notice the image page specifies that the image is being used under fair use but there is no explanation or rationale as to why its use in this Wikipedia article constitutes fair use. In addition to the boilerplate fair use template, you must also write out on the image description page a specific explanation or rationale for why using this image in each article is consistent with fair use.

Please go to the image description page and edit it to include a fair use rationale. Using one of the templates at Wikipedia:Fair use rationale guideline is an easy way to insure that your image is in compliance with Wikipedia policy, but remember that you must complete the template. Do not simply insert a blank template on an image page.

If there is other fair use media, consider checking that you have specified the fair use rationale on the other images used on this page. Note that any fair use images uploaded after 4 May, 2006, and lacking such an explanation will be deleted one week after they have been uploaded, as described on criteria for speedy deletion. If you have any questions please ask them at the Media copyright questions page. Thank you.

BetacommandBot 11:24, 6 July 2007 (UTC)

[edit] Minimum area?

I don't believe the several-times-repeated minimum area bit.

Clearly this isn't true for bubbles (its min area for a given volume).

Observationally, it isn't true for cylindrical films supported by circles above and below (they bow in at the middle; I think I understand this thinking about balance of forces: if the film *was* cylindrical the up-and-down forces would cancel in the middle but the around-forces would both be pulling inwards, and it would bow in. And indeed it does).

William M. Connolley 23:04, 11 July 2007 (UTC)