| MadSci Network: Physics |
There are (at least) two effects in play with this phenomenon. One is the instability of the straw at the upper edge of the container, and the other is the loss of carbonation from the drink. By the way, there is a previous answer in our archives which discusses some of the aspects of the actual formation of bubbles on the straw, so I will not touch on that subject directly.
Concerning the first effect, if the liquid's surface is closer to the top of the container then the straw doesn't have to be as far out of the fluid before it can tip over the edge of the container. When the center of mass of the straw gets as high as the container's edge then the straw can tip out.
The second effect results in less bubbles on the straw as time goes on, so the straw probably doesn't float as high later. The carbonation is lost as carbon dioxide leaves the drink, and is the reason why carbonated drinks go flat. There are some previous answers in our archives dealing with flat drinks, which you can find by using our search engine to search on "drink flat" with "whole words" turned off.
John Link, MadSci Physicist
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