Re: Why do diet coke cans float and regular coke cans sink?

Hannah:

I must first give you credit for your observation. I have been drinking diet coke for years and my wife, regular coke, and I have never took notice to which, if any can floats and which can sinks. I only regret that I did not have any cans of each on hand to observe it for myself. As to the cause, it may be one of two things and some testing would be needed to tell for sure. This may be an interesting little research project for your school class. Ask your teacher, and let him or her read this to understand why it might make a neat little project.

First the cause could be the bottler, the particular company location which mixes up the coke and fills the cans, or it may the coke formulation itself. I will attempt to explain. The property which makes something float is called bouyancy. If a can of diet coke floats than the weight of the can, plus air in the can, plus soda in the can, must weigh less than the weight of water displaced by the can. For a can of regular coke to sink, then the weight of the can, plus the weight of air in the can, plus the weight of the soda must weight more than the water displaced by the can. If we assume that the weight of the can itself is the same for coke or diet coke cans, then either the amount of air in the two cans is different or the density of the two sodas is different, or both. (I will explain what density is in a minute). This is how the bottler could be the cause. If the volume of each can is identical (which it probably is), then if the bottler's equipment just happens to put a bit less diet coke in the diet-coke cans compared to regular coke in regular-coke cans, then the amount of air space in each is different which could make the diet coke cans float. This is why coke from other bottlers needs to be checked. If you have any family or friends in another state, their coke probably comes from a different bottler, and could be checked to see if it behaves the same.

The other cause could be the coke formulation itself. Artificial sweeteners are more concentrated than sugar. You need less weight of the sweetener compared to sugar, to make the product sweet. Because less weight of sweetener is very likely dissolved in diet coke, compared to sugar in regular coke, then the weight of diet coke is less than regular coke for the same unit volume. This is the property called density, weight per unit volume. Water happens to have a density of 62 pounds per cubic foot. It's pretty heavy when you think about it. Because coke is mostly water and anything added to it would make it heavier than water, then both coke and diet coke would both be heavier than water and would make the can want to sink. You must however look at everything together. Diet coke probably weights a bit less than regular coke per unit volume, then the combined density of a can of diet coke could be slightly less than a can of regular coke, and because both cans are the same size and shape and would displace the same amount of water in your cooler, then it would be more likely that the can of diet coke would be more prone to float. However because the air space in a can has a much lower density than water, slight differences in the amount of this air space would have a big effect on the overall density of the can. Look at the two- litter bottles of soda in the grocery store; they are not all filled to exactly the same level, close but not exactly the same. This is why product from different bottlers should be checked. I also do not know if bottlers fill containers by measuring weight or volume. This to could be a factor.

As for me, I would continue to perform this check from time to time, and ask other friends or relatives out-of-state to do the same. I myself bet that it is the bottler, not the coke product. However I could be wrong, but either way I believe that diet coke would be the one more likely to float. Sorry I could not be more exact with my answer. Keep exercising your observational skills, you could make a great scientist someday. As Bill Nye often says.. "Science Rules".

Greg Dries