Black Haired Girl Making Soap Bubbles Down By The Lake

Physics
Surface tension and shape
A soap 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. Soap film is extremely flexible and can produce waves based on the force exerted. 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, soap actually 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 in turn causes the surface tension to increase. Thus soap works by selectively strengthening the weakest parts of the bubble, preventing any one part of the bubble from stretching excessively. In addition, soap reduces evaporation, making the bubbles last longer; but this effect is relatively small.
The spherical shape of a bubble is also due to surface tension. The sphere has the smallest possible surface area for a given volume, thus taking up a spherical shape minimises the free surface of a bubble. This shape can be visibly distorted by air currents. However, if a bubble is left to sink in still air, it remains rather 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.)