Ask-a-Physicist
A ninth grader wants to know what it's like to be a physicist. Here is one physicist's response.
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On Saturday, I accidentally left a full cup of diet soda sitting in my car. It was originally full of ice, which of course melted over the course of a day and a half. When I got into my car on Monday morning, the straw was just over half full of soda, extending about 2" above the full level of soda in the cup. This condition held constant for quite some time, even when the cup was lifted and jiggled/disturbed. Once I had taken a tiny sip, the level of soda in the straw went back down to where I would have expected to find it (at the same level as the soda in the cup). Given that this was a standard lid (with an opening at the top for the straw that is certainly not airtight, nor was the top opening of the straw airtight at all) I could not imagine how the soda in the straw was being pushed or pressured to a higher level than the soda in the cup. The weather over the weekend was cold, but not freezing, averaging in the low 50's. Why did the liquid level in the straw from my soda rise above the liquid in the cup after being left in my car for the weekend? Find out the answer »
