Soap Bubble Pressure: Why Does It Decrease?

[phymatter]

if air is pushed inside a soap bubble then why does the pressure decrease ?

 

[cragar]

This might help, this is a thread that talks about the pressure inside a soap bubble.
https://www.physicsforums.com/showthread.php?t=38784

 

[Bill_K]

Because if you add air to the bubble its size will increase. Bigger bubble means the surface is less curved, and the curvature of the surface is what causes the additional pressure inside.

 

[Andy Resnick]

Recall a soap bubble has *two* interfaces- the exterior air-soap interface and the interior soap-air interface.

The total pressure jump between the inside and outside air is this dependent on the difference in curvatures between the two interfaces (and the thickness of the soap film). As the bubble is expanded, the film thins, the two surfaces approach the same value of curvature, and the total pressure jump approaches zero.

 

[Bill_K]

The typical thickness of the walls of a soap bubble is about a micrometer, regardless of the diameter of the bubble. I don't really see how the tiny difference in curvature between the inside and the outside would matter.

 

[Andy Resnick]

The typical thickness of the walls of a soap bubble is about a micrometer, regardless of the diameter of the bubble. I don't really see how the tiny difference in curvature between the inside and the outside would matter.

Fortunately, science cares not a whit about what you think makes sense. Clearly, the soap film varies in thickness as the bubble changes size; also clearly, the two radii of curvature are different. Laplace's equation does the rest.

 

[cragar]

this is a really cool video about soap bubbles

He does demos and explains a little bit about the physics of soap bubbles.