How does an air bubble have 2 surfaces and a liquid drop has 1 surface? My teacher told me that an air bubble has 2 surfaces and a liquid drop has only 1 which is the reason for the air bubble having twice the pressure difference as a liquid drop with same surface tension. But I couldn't get it how an air bubble has 2 surfaces isn't it just 1 spherical surface ? Please help
 A: A air bubble is hollow inside it.
It doesn't pop or pops just due to pressure difference inside it and outside it.
Hence it has 2 surfaces- the inside one and outside one
While water drop has only one surface i.e the outside one
A: Think about what a microscopic observer would experience as they moved from somewhere outside the bubble to its centre.
With an air bubble they go from air (outside) to water (the "shell" of the bubble) to air again (centre). So they pass through two surfaces.
With a water drop they go from air (outside) to water (all the way from the surface of the drop to its centre). So they only pass through one surface.
A: Think bubble as a bag.
A bubble is an empty bag. The bubble has an inside and outside.
The drop is a bag full filled with the same material of the membrane.
A: I think there is a little confusion here between a bubble and a membrane.
What is referred here as an air bubble, is actually a membrane of liquid form enclosing a volume of gas, and floating inside another volume of gas (usually air).
And what people refer to as air bubbles, is this membrane, which like any other membrane has two surfaces, while a pure air bubble inside any liquid has only one surface.
A: This video will surely help
https://youtu.be/Us7sk1OrcUc
Watch at high speed( at least 1.5x)
A: If a bubble has same inner an putter environment like an air bubble or soap bubble then it has 2 surfaces
If the bubble has two different environment on the inner and outer side like water drop in air or air bubble in water then it has 1 surface
