The —getting a water bottle to land just right, and then overreacting to it—is enjoyable not only because it demonstrates skill, but also because it shows off basics properties of physics. Flippers must master the way water moves around in the bottle during the flip.
But what if the stuff inside the bottle wasn't water at all? Popular YouTuber BackyardScientist is here to find out. *This is an experiment you should absolutely never attempt yourself.
When using mercury, BackyardScientist shows how valuable weight distribution can be to a proper flip (or trying to do anything else, for that matter). Because of mercury's added weight, at a certain point it's impossible to drop a water bottle filled with it and have the bottle land right-side up. All that weight at the bottom, with only the bottle as a cushion, leaves nowhere for the energy to transfer. The bottle just bounces off.
Only with weight distribution throughout the bottle, and perfect timing, can the mercury land. Once BackyardScientist gets the hang of it, it becomes easier for him to use the poisonous metal.