How physics lets a toy boat float upside down
Buoyancy will keep objects afloat on the underside of a levitating liquid
An antigravity effect in the lab allows toy boats to float upside down on the underside of levitating liquid.
B. Apffel et al/Nature 2020
Going bottom-up is no problem for a boat on the underside of a levitating liquid.
In a container, liquid can be levitated over a layer of gas by shaking the container up and down. The upward jerking motion keeps fluid from dripping into the air below. Now, lab experiments have revealed a curious side-effect of this phenomenon. Objects can float along the bottom of this levitated liquid.
Emmanuel Fort is a physicist at the École Supérieure de Physique et de Chimie Industrielles. It’s in Paris, France. Fort was part of a team that levitated silicone oil or glycerol. Then the researchers watched as toy boats bobbed along the top — and bottom — of the hovering liquid.
A toy boat floating atop the liquid experienced buoyancy. This force pulled the boat upward toward the sky. The strength of the force depended on the amount of space the boat took up in the liquid. It’s a physical law discovered by Archimedes (Ar-kih-MEE-deez). The inventor and mathematician lived in ancient Greece. His law explains why dense objects sink and lightweight objects float.
An upside-down boat, it turns out, experiences the same upward pull. As long as the right amount of the boat is submerged in the liquid, the buoyant force will be strong enough to offset the gravity pulling the boat down. As a result, the underside boat floats, too. (Bet Archimedes never saw that coming.)
Whatever floats your boat
Partially sunk toy boats on the top and bottom surfaces of a levitated liquid (illustrated) experience the upward force of buoyancy. That force offsets gravity’s downward pull, allowing the toys on both sides of the liquid’s surface to float.
Buoyancy explains how a top-down boat floats on levitated liquid
Source: B. Apffel et al/Nature 2020
The team reported its finding September 3 in Nature.
Vladislav Sorokin was surprised to see the effect. He is an engineer in New Zealand at the University of Auckland. Sorokin has studied why bubbles sink to the bottom of levitated liquids rather than float to the top. The new finding, he says, now hints that other weird effects are waiting to be discovered in levitating systems.
