1. Because the bubble is like a balloon. It's got air inside. When it close to trap air in, nothing can go in and out. (เดี๋ยวเกิดถามว่าทำไมบางลูกมีน้ำอยู่ข้างใน)
ถามกลับเลยเพราะลูกยังไม่หายสงสัยหรอกว่าทำไมน้ำเข้าไปไม่ได้
What happen with the balloon when you open it? (นึกออกไหมค่ะ เวลาที่ปล่อยปากลูกโป่งนะค่ะ) รอให้เด็กตอบนะค่ะ
The air inside will get out and the balloon will get smaller.
The bubble is more delicate than the balloon. The bubble skin is make from soapy water. It doesn't have the airway for you to blow the air in. like the balloon. So if you break/pop it and let the air out, it's gone.
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. 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. So 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.
The 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. 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.)