Mercury is such a dense liquid that cannonballs float in it. Humans float on it too (you'll have to scroll down a bit for the picture), but it's probably not a good idea. If you just can't resist hopping in the mercury vat, elemental mercury is less likely to kill you than mercury compounds. It used to be sold as a laxative (officially branded Dr. Rush's Bilious Pills but colloquially known as "thunder clappers"); Lewis and Clark's campsites can sometimes be identified by the mercury they deposited along the way.
Levitated Interaction Element Move, record and playback a ball along a path in a three-dimensional space.
Making water appear to levitate usually requires a strobe light to trick the eye. If you don't have a fancy system to control water flow, you can run water through a tube taped to a speaker playing very low frequency sound, and again use a strobe light to make the water appear to defy gravity. Or you can ditch the strobe, and sync the sound waves to the frame rate of a video camera to make water drops appear to hover.
Does it suck? Or does it rock? No, this is NOT like Will It Float? or Will It Blend? It's a cute use of the Google API to search for how often your inquiry comes up as "x sucks" or "x rocks" or a small number of other similar phrases. MetaFilter rates 8.7 out of 10 (87% rocks, 13% sucks). A delightfully evil way to rate - and compare - various things.
Float (youtube) is the first of a series of short films designed to stir the imagination. The brief film shows the streets of Melbourne as the letters & numbers from every sign in town begin to peel off & float away on the wind. The project lives here, and open contributions are being listed here.