A soap bubble is a very thin film of soap water that forms a sphere with an iridescent surface. Soap bubbles usually last for
only a few moments and then burst either on their own or on contact with another object. They are often used as a children's
plaything, but their usage in artistic performances shows that they can be fascinating for adults too.Soap bubbles can help
to solve complex mathematical problems of space, as they will always find the smallest surface area between points or
edges.

A bubble can exist because the surface layer of a liquid (usually water) has a certain surface tension, which causes the
layer to behave somewhat like an elastic sheet. However, a bubble made with a pure liquid alone is not stable and a
dissolved surfactant such as soap is needed to stabilize a bubble. A common misconception is that soap increases the
water's surface tension. Actually soap does the opposite, decreasing it to approximately one third the surface tension of
pure water. Soap does not strengthen bubbles, it stabilizes them, via an action known as the Marangoni effect. As the soap
film stretches, the surface concentration of soap decreases, which causes the surface tension to increase. Thus, soap
selectively strengthens the weakest parts of the bubble and tends to prevent them from stretching further. In addition, the
soap reduces evaporation so the bubbles last longer, although this effect is relatively small.

Their spherical shape is also caused by surface tension. The tension causes the bubble to form a sphere, as a sphere has
the smallest possible surface area for a given volume. This shape can be visibly distorted by air currents, and hence by
blowing. If a bubble is left to sink in still air, however, it remains very nearly spherical, more so for example than the typical
cartoon depiction of a raindrop. When a sinking body has reached its terminal velocity, the drag force acting on it is equal to
its weight. Since a bubble's weight is much smaller in relation to its size than a raindrop's, its shape is distorted much less.
(The surface tension opposing the distortion is similar in the two cases: The soap reduces the water's surface tension to
approximately one third, but it is effectively doubled since the film has an inner and an outer surface.)

Source: WikepediA
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