I was at a party and there was a huge tub of drinks, all the regular sodas sank to the bottom, but the diet variety floated at the top. What gives?
I guess they have less density because they are missing some of the stuff that makes’em good. Just wandering what it is.
The regular soda is heavier than the diet soda. Reason being is because there is more sugar in the regular soda, which increases the density. It becomes more dense than the water, so it sinks.
The diet soda has artificial sweetner in it. Since this is not as dense as the sugar is, the can floats. This is a common experiment in high school chemistry classes. This is one of the experiments I remember quite well.
The reason my Chemistry teacher gave (she did this as a demonstration in class) was that the sugar (or corn syrup) is heavier than Nutrasweet, so the diet soda as a whole is less dense, and therefore floats. She also demonstrated this with a Coors Light (floated really good because of the alcohol) and a Guiness (super-carbonation + alcohol–floats like a cork). Isn’t Chemistry fun? 
Sugar isn’t necessarily heavier than Nutrasweet, it is that Nutrasweet is much sweeter than sugar. Therefore, less of it (e.g. mass) is needed to sweeten a diet soda to the level of sweetness you are accustomed to in the regular stuff.
This amounts to the same thing as saying sugar is heavier, I suppose, but we might as well be clear on why.