Asoap bubble (commonly referred to as simply abubble) is an extremely thinfilm ofsoap ordetergent and water enclosing air that forms a hollowsphere with aniridescent surface. Soap bubbles usually last for only a few seconds before bursting, either on their own or on contact with another object. They are often used for children's enjoyment, but they are also used in artisticperformances. Assembling many bubbles results infoam.
When light shines onto a bubble it appears to change colour. Unlike those seen in arainbow, which arise from differential refraction, the colours seen in a soap bubble arise from lightwave interference, reflecting off the front and back surfaces of the thin soap film. Depending on the thickness of the film, different colours interfere constructively and destructively.
Soap bubbles are physical examples of the complexmathematical problem ofminimal surface. They will assume the shape of leastsurface area possible containing a given volume. A true minimal surface is more properly illustrated by asoap film, which has equal pressure on both sides, becoming a surface with zeromean curvature. A soap bubble is a closed soap film: due to the difference in outside and inside pressure, it is a surface ofconstant mean curvature.
While it has been known since 1884 that a spherical soap bubble is the least-area way of enclosing a given volume of air (a theorem ofH. A. Schwarz), it was not until 2000 that it was proven that two merged soap bubbles provide the optimum way of enclosing two given volumes of air of different size with the least surface area. This has been dubbed thedouble bubble conjecture.[1]
Because of these qualities, soap bubble films have been used in practical problem solving applications.Structural engineerFrei Otto used soap bubble films to determine the geometry of a sheet of least surface area that spreads between several points, and translated this geometry into revolutionarytensile roof structures.[2] A famous example is his West German Pavilion at Expo 67 in Montreal.
The structures that soap films make can not just be enclosed as spheres, but virtually any shape, for example in wire frames. Therefore, many different minimal surfaces can be designed. It is actually sometimes easier to physically make them than to compute them bymathematical modelling. This is why the soap films can be considered asanalog computers which can outperform conventional computers, depending on the complexity of the system.[3][4][5]
When two bubbles merge, they adopt a shape which makes the sum of their surface areas as small as possible, compatible with the volume of air each bubble encloses. If the bubbles are of equal size, their common wall is flat. If they are not the same size, their common wall bulges into the larger bubble, since the smaller one has a higher internalpressure than the larger one, as predicted by theYoung–Laplace equation.
At a point where three or more bubbles meet, they sort themselves out so that only three bubble walls meet along a line. Since the surface tension is the same in each of the three surfaces, the three angles between them must be equal to 120°. Only four bubble walls can meet at a point, with the lines where triplets of bubble walls meet separated by cos−1(−1/3) ≈ 109.47°. All these rules, known asPlateau's laws, determine how afoam is built from bubbles.
The longevity of a soap bubble is limited by the ease of rupture of the very thin layer of water which constitutes its surface, namely amicrometer-thicksoap film.It is thus sensitive to :
After experiments, researchers found that a solution containing:
gave the longest lasting results as it minimised theMarangoni Effect.[6]
When a soap bubble is in contact with a solid or a liquid surfacewetting is observed. On a solid surface, thecontact angle of the bubble depends on thesurface energy of the solid.[7][8] A soap bubble has a larger contact angle on a solid surface displayingultrahydrophobicity than on a hydrophilic surface – seeWetting. On a liquid surface, the contact angle of the soap bubble depends on its size - smaller bubbles have lower contact angles.[9][10]
The liquid shell of a soap bubble is heavier than air. However the gas inside a bubble typically contains more water vapor than the surrounding air. Water vapor isless dense than dry air, which can give the bubble positive buoyancy. This can be increased by using warm liquid, since this increases the temperature of the gas inside the bubble and therefore decreases its density.
Soap bubbles have been used as entertainment for at least 400 years, as evidenced by 17th-century Flemish paintings showing children blowing bubbles with clay pipes. The London-based firmA. & F. Pears created a famous advertising campaign for its soaps in 1886 using a painting by John Everett Millais of a child playing with bubbles. The Chicago company Chemtoy began selling bubble solution in the 1940s, and bubble solution has been popular with children ever since. According to one industry estimate, retailers sell around 200 million bottles annually.Dishwashing liquid with water and additional ingredients such asglycerin andsugar is used as a popular alternative to a ready made bubble solution.[11]
A bubble is made of transparent water enclosing transparent air. However, thesoap film is as thin as the visible lightwavelength, resulting inoptical interference. This createsiridescence which, together with the bubble's spherical shape and fragility, contributes to its magical effect on children and adults alike. Each colour is the result of varying thicknesses of soap bubble film.Tom Noddy (who featured in the second episode ofMarcus du Sautoy'sThe Code) gave the analogy of looking at acontour map of the bubbles' surface. However, it has become a challenge to produce artificially coloured bubbles.
Byron, Melody & Enoch Swetland invented a patented non-toxic bubble (Tekno Bubbles)[12] that glow under UV lighting. These bubbles look like ordinary high quality "clear" bubbles under normal lighting, but glow when exposed to true UV light. The brighter the UV lighting, the brighter they glow. The family sold them worldwide, but has since sold their company.
Adding coloureddye to bubble mixtures fails to produce coloured bubbles, because the dye attaches to the water molecules as opposed to the surfactant. Therefore, a colourless bubble forms with the dye falling to a point at the base. DyechemistDr. Ram Sabnis has developed alactone dye that sticks to the surfactants, enabling brightly coloured bubbles to be formed.Crystal violet lactone is an example. Another man named Tim Kehoe invented a coloured bubble which loses its colour when exposed to pressure or oxygen, which he is now marketing online asZubbles, which are non-toxic and non-staining. In 2010, Japanese astronautNaoko Yamazaki demonstrated that it is possible to create coloured bubbles inmicrogravity. The reason is that the water molecules are spread evenly around the bubble in the low-gravity environment.
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If soap bubbles are blown into air that is below atemperature of −15 °C (5 °F), they will freeze when theytouch a surface. The air inside will graduallydiffuse out, causing the bubble to crumble under its own weight. At temperatures below about −25 °C (−13 °F), bubbles will freeze in the air and may shatter when hitting the ground. When a bubble is blown with warm air, the bubble will freeze to an almost perfect sphere at first, but when the warm air cools, and a reduction in volume occurs, there will be a partial collapse of the bubble. A bubble, created successfully at this low temperature, will always be rather small; it will freeze quickly and will shatter if increased further.[13]Freezing of small soap bubbles happens within 2 seconds after setting on snow (at air temperature around –10...–14 °C).[14]
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Soap bubbleperformances combineentertainment with artistic achievement. They require a high degree of skill.[citation needed] Some performers use common commercially available bubble liquids while others compose their own solutions. Some artists create giant bubbles or tubes, often enveloping objects or even humans. Others manage to create bubbles forming cubes, tetrahedra and other shapes and forms. Bubbles are sometimes handled with bare hands. To add to the visual experience, they are sometimes filled withsmoke, vapour orhelium and combined withlaser lights or fire. Soap bubbles can be filled with a flammable gas such asnatural gas and then ignited.
Professional bubble artists includeTom Noddy,Fan Yang andThe Amazing Bubble Man.
Bubbles can be effectively used to teach and explore a wide variety of concepts to even young children. Flexibility, colour formation, reflective or mirrored surfaces, concave and convex surfaces, transparency, a variety of shapes (circle, square, triangle, sphere, cube, tetrahedron, hexagon), elastic properties, and comparative sizing, as well as the more esoteric properties of bubbles listed on this page. Bubbles are useful in teaching concepts starting from 2 years old and into college years. A Swiss university professor, Dr. Natalie Hartzell, has theorized that the usage of artificial bubbles for entertainment purposes of young children has shown a positive effect in the region of the child's brain that controls motor skills and is responsible for coordination with children exposed to bubbles at a young age showing measurably better motion skills than those who were not.[15]
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