A can of normal coke or pepsi contains a lot of sugar in a fixed volume of aerated or carbonated water. Whereas a can of diet-coke or diet-pepsi contains a tiny amount of the artificial sweeteners saccharin, acesulfame, aspartame, neotame, and sucralose. These artificial sweeteners give the same amount of sweetness as a few grams of sugar. Thus, the diet-coke or diet-pepsi has less density relative to water than a normal can of coke or pepsi. Thus, a can of greater density than water sinks while the diet-coke/pepsi can floats.
