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Seminario di Dipartimento: Levitation, oscillation and wave propagation in a stratified fluid (video disponibile)

Videoregistrazione disponibile

12 Novembre 2021– 14:30

Dipartimento di Fisica, Università di Milano

Levitation, oscillation and wave propagation in a stratified fluid

AULA A in presenza e in streeming


Levitation of macroscopic objects occurs when a body floats in stable equilibrium
inside a fluid. This puzzling phenomenon has fascinated humankind for a very long
time and is still the topic of cutting-edge research works. It hardly occurs
spontaneously in nature and is extremely difficult to observe on Earth due to the
presence of gravity. However, a condition similar to levitation may occur in a stably
stratified fluid. Under these conditions, an object can stay at rest at a height where
its density and that of the fluid are perfectly matched. When this object is moved
from its position, a restoring force tends to bring it back to the initial place and the
body oscillates and emits mechanical waves in the surrounding fluid. Even more
surprising is the case of a body, initially at rest that suddenly starts to rise as pushed
by an invisible force. This phenomenon may occur when an object is placed in a
fluid where a concentration gradient is developing in time.
In this talk we will discuss a simple but intriguing experiment done with everyday
objects that allows to show such a sudden levitation phenomenon and is able to
catch many aspects related to the physics of a stratified medium, such as the Brunt-
Väisälä oscillations occurring in the atmosphere and in stars, and the propagation of
internal gravity waves inside the stratified medium.

Students are cordially invited

Contact silvia.leoni@mi.infn.it


12 novembre 2021
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