A can of Diet Coke and a can of (regular) Coca Cola are placed side-by-side in a container of water.  A mask has been electronically inserted to cover up the Coca Cola can, as seen in the photograph below. The Diet Coke can is just barely floating, as can be seen in the photograph.


Assuming that there is the same volume of both drinks in their respective (identical in size and shape) cans, the question this week involves how the regular Coca Cola will float relative to the Diet Coke.

The regular Coca Cola can will:

  • (a) float higher in the water than the Diet Coke.
  • (b) float at the same level as the Diet Coke.
  • (c) float lower in the water than the Diet Coke.
  • (d) sink.

To see the answer, click Read More on 12/26/14

The answer is (d): the regular Coca Cola can will sink, as seen in the photograph below with the mask removed.


When sugar is dissolved in water, it partially occupies the spaces between water molecules, so the density of sugar water is somewhat greater than that of regular water.  Lots of sugar can be dissolved in water with only a small increase in volume.  On the other hand, it only takes a small amount of artificial sweetner to sweeten a diet drink, so its density is only slightly heavier than water.  Therefore the regular Coca Cola will sink.

Give yourself half credit if you said the Coca Cola will float lower than the Diet Coke.  Buoyancy is a very tenuous matter: virtually as soon as the density of an object becomes greater than that of water, it will sink to the bottom in water.  Despite the old movies, it is virtually impossible that a boat would ever have exactly the necessary density to do anything but float on the surface of the ocean or sink to the bottom.