Toy boats float upside down underneath a layer of levitated liquid
Going bottom-up is no problem for a boat on the underside of a levitated liquid. In a container, liquid can be levitated over a layer of gas by shaking the container up and down because the repeated, upward jerking motion keeps fluid from dripping into the air below. Lab experiments have revealed a curious consequence of this antigravity effect. Objects can float along the bottom of a hovering liquid as well as along the top, researchers report in the Sept. 3 Nature. Physicist Emmanuel Fort and colleagues observed this effect by injecting a layer of gas underneath either silicone oil or glycerol and shaking the container. The researchers used these thick substances because keeping a liquid aloft requires vigorous shaking — with larger pools requiring stronger vibrations — and a runny fluid like water would slosh around too much to form a stable, levitated layer. “Technically, you could have a liquid pool of...