Suppose you could get a layer of liquid to stay suspended in mid-air, then you could observe counter-intuitive things such as objects like toy boats floating on both the top and bottom surfaces, being right side up on the top surface and upside down on the bottom surface.
But how could you get such a layer of liquid to defy gravity in this way? It turns out you can, as can be seen in this video.
This article explains how it was done.
If a container holding a runny liquid is swiftly flipped over, the liquid will fall to the bottom. The liquid does not fall in one go, however. Instead, droplets first form on the underside of the liquid, which instigate the rest of the liquid’s collapse.
But set the container on a vibrating plate and the liquid can behave very differently. Vertical shaking at the right frequency prevents the droplets forming. Without them, the liquid remains aloft: instead of falling, it rests on the cushion of air.
This much was already known. What Fort and his colleagues showed was that objects could experience an “antigravity” effect and float in the underside of the levitated liquid. Writing in Nature, they demonstrate this with small toy boats floating in levitating layers of glycerol and silicon oil.
A number of forces keep the boats in place. The first comes from air pressure, which is raised by the weight of the liquid above, and pushes the boat up into the water. But the liquid pushes back on the boat itself, a force that decreases higher up the layer. Gravity also pulls the boat down. It all makes for a delicate balance that could fall apart at any moment, were it not for the vibrations.
The paper on which the above newspaper article is based was published in the journal Nature and can be read here.
Physicists just wanna have fun!