In France, Physicists have managed to make objects float upside down! It looks almost as if gravity is non-existent. This was done by placing them on the underside of a highly viscous liquid. In spite of the fact that this discovery complies with the laws of physics, it could potentially help us understand liquid-gas interactions to a much greater extent.
Archimedes’ principle says that an object fully or partially immersed in a liquid experiences the upward force of buoyancy, which is equal to the weight of liquid it displaces. Since the direction of this buoyant force is opposite to that of gravity, objects less dense than the liquid float and top of it, and denser than the liquid, it sinks.
We experience this phenomenon in our everyday lives. Liquids usually exist at a lower gravitational potential than gases. For example, when we travel by boat we travel both
through the air and through the sea. However, the sea is lower than the water.
Scientists hypothesise that in an upside down world, where the liquid is above the gas, objects will still float on the liquid, appearing to fly.
The secret to achieving this effect is vibrations. Since the 1950s, scientists have demonstrated a range of counter-intuitive effects by vibrating fluids at high frequencies. Vibrations can make whole layers of liquid float in air. This is because liquids tend to drip due to gravity, causing gas to be on top. However, vibrations can prevent liquids from forming drops, thus causing them to float in air.
Physicists at the PSL University in Paris fixed a plexiglass container to a vibrating platform and then filled the container with either silicon oil or glycerol. After turning the shaker on, the researchers used a syringe with a long needle to inject air towards the bottom of the liquid. With the resulting bubble sinking and growing, it eventually created a layer of air across the bottom of the container – causing the viscous liquid to levitate.
This fluid levitation is nothing new. However, what these physicists then did was to place objects upside-down on the lower interface between the liquid and the air. This works on the same principle as regular buoyancy, gravity pulls it down and the disturbance it creates in the liquid pulls it upwards. However, this looks absolutely extraordinary!
However, there is an important difference between regular and upside down floating. If a regularly floating object is moved, it displaces a greater amount of liquid and so experiences more buoyancy, while any force pushing it out of the liquid will be opposed by gravity. But in the upside-down case, any slight displacement from equilibrium will see the object accelerate away – thanks to gravity below and the mass of liquid above.
This discovery looks remarkable and opens several new doors in liquid gas interactions!