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Question
Will a soda can that is filled with distilled water float or sink in distilled water?  

My guess is that the can will sink.  So why do diet soda cans float when they are filled with liquid?  Isn't the density of carbonated water greater than uncarbonated water?  Or is there a little bit of free CO2 gas in the can that keeps it afloat for diet soda?  (I'm aware that regular soda cans sink because of increased density from corn syrup.)

Answer
There's a whole page about this... http://www.aqua-calc.com/page/density-table/substance/carbonated-blank-beverage-  The density of carbonated water is indeed slightly higher than that of water.  If a can is totally filled with no gap, it would (of course) sink in regular water, even if it were diet soda.  Basically, physics says you're correct in general...but I've also seen diet sodas sink (might depend on the size of the amount of gaseous CO2 in the can).

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Dr. Stephen O. Nelson

Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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