

Why is the sky blue? What is lightning? What are the states of matter? Does hot water freeze faster than cold? Why does a can of Coke sink while a can of Diet Coke floats? Why do you close your eyes when you sneeze? Why do mosquitoes bite me more than my friends? Why do your feet stink? How does gravity work? How fast does the space shuttle move in orbit? What is escape velocity? What would happen if you turned on your headlights while moving at the speed of light?

Why does a can of Coke sink while a can of Diet Coke floats?

Floating occurs because floating objects displace, or push aside, a certain amount of liquid. If an object displaces more than its weight in liquid, it floats; otherwise it sinks. Density (the mass per unit of volume) determines how much liquid is displaced. Density is usually compared to water, which is assigned a density of 1. Materials sink if (like regular Coke) they are more dense than water, while less-dense materials, like Diet Coke, float. Actual photograph of the experiment as performed in the Why Files lab! Note the Diet Coke breaking the surface on the left. We didn't ask the Coca Cola Co. for their recipe, but we assume that it's the sugar in real Coke that makes it dense enough to sink. We also assume that it's the artificial sweetener in that diet version that's less dense, allowing those cans to float. Did you know

If you measure the volume of water displaced by a floating object and compute the weight of that water, it equals the weight of the object.