Why a Diet Coke floats while regular Coke sinks in water
In short: If you drop both into a tank, the Diet Coke will bob on the surface while the regular version sinks. It seems to defy physics since both cans are identical in size and volume, but the secret lies in the chemistry of what is inside.
The phenomenon is a classic demonstration of buoyancy and specific gravity. According to the principles of physics, an object will float if it displaces a weight of liquid greater than its own weight. In this scenario, the aluminum cans and the compressed gas inside them have nearly identical masses and volumes, meaning the outcome depends entirely on the density of the liquid contents. This occurs because an object floats when it displaces a sufficiently dense gas or liquid that weighs more than itself. Even though the printed volume on the label is 355 mL, the actual liquid content is often slightly less.
Regular Coca-Cola contains a significant amount of dissolved sugar. For a typical can, this might consist of approximately 39 grams of sugar dissolved in 352 mL of liquid. This high concentration of solutes increases the liquid's density to about 1.026 g/mL. Because this density is higher than that of water, the regular Coke can remains submerged.
Diet Coke, however, lacks this sugar load. Experiments show its liquid density is significantly lower, averaging around 0.911 g/mL. Because this is less dense than water, the Diet Coke can achieves buoyancy and floats. While a prankster might try to make a regular Coke float by trapping an air bubble under the concave bottom of the can, a simple nudge will release the bubble and reveal the truth.
This experiment highlights how small changes in chemical composition can radically alter the physical properties of a substance, turning a sinking object into a floating one without changing its external dimensions.
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Sources
- Summary by Intellect · source: Why Do Cans of Diet Coke Float and Coke Don't?
- Also: Coke Can Buoyancy | Harvard Natural Sciences Lecture Demonstrations
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