# Time taken by a balloon to deflate

**1. The problem statement, all variables and given/known data**

A soap bubble is blown with a relatively short drinking straw of diameter d, and then the bubble is left to deflate through the same straw. In one case when the diameter of the bubble was D the time during which the bubble deflated was 8 seconds. Estimate the time during which a bubble deflates

a) if its diameter is also D, and it is deflated through a wider straw of diameter 2d;

b) through a straw of diameter d, if its greatest diameter was 2D?

**2. Relevant equations**

**3. The attempt at a solution**

The air inside the bubble moves out because of the pressure difference between the two ends of straw. The pressure difference is ##4T/r##, where ##T## is the surface tension of soap liquid and ##r## is the radius of bubble at any time. I feel I have to find the time (##dt##) in which the radius of bubble decreases by ##dr## and then integrate it but how do I find an expression for ##dt##? :confused:

Any help is appreciated. Thanks!

http://ift.tt/MVFEVS

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