Sink-Float-Repeat: The primary value of this simple demonstration is for students to closely observe and then try to explain what is happening in this unusual system in motion.
Objects sink when they are denser than the liquid that surrounds them. However, an object that sinks initially can be enticed to float if its density is decreased. When objects are added to carbonated drinks, the objects may initially be denser than the surrounding liquid. As carbon dioxide bubbles collect around the object, the density of the object decreases. As a result, it starts to rise through the now less dense liquid until it reaches the top. Once it reaches the top, the gas bubbles are released, the object becomes heavier and sinks again to the bottom. The cycle continues until the carbonation lessens. Key Concepts: sink, float, light, heavy, gases, liquids, density