We present an engaging levitation experiment that students can perform at home or in a simple laboratory using everyday objects. A cork, modified to be slightly denser than water, is placed in a jug containing tap water and coarse kitchen salt delivered at the bottom without stirring. The salt gradually diffuses and determines a stable density stratification of water, the bottom layers being denser than the top ones. During the dissolution of salt, the cork slowly rises at an increasing height, where at any instant its density is balanced by that of the surrounding water. If the cork is gently pushed off its temporary equilibrium position, it experiences a restoring force and starts to oscillate. Students can perform many different measurements of the phenomena involved and tackle non-trivial physical issues related to the behaviour of a macroscopic body immersed in a stratified fluid. Despite its simplicity, this experiment allows to introduce various theoretical concepts of relevance for the physics of the atmosphere and stars and offers students the opportunity of getting acquainted with a simple system that can serve as a model to understand complex phenomena such as oscillations at the Brunt–Visl frequency and the propagation of internal gravity waves in a stratified medium.

我们展示了一个引人入胜的悬浮实验，学生可以在家里或在简单的实验室中使用日常用品进行这项实验。将软木塞放入比水略重的软木塞中，放入装有自来水和粗食盐的壶中，底部不经搅拌。盐分逐渐扩散并确定水的稳定密度分层，底层比顶层密度大。在盐的溶解过程中，软木塞随着高度的增加而缓慢上升，在任何时刻，它的密度都与周围的水的密度相平衡。如果软木塞被轻轻推离其临时平衡位置，它会受到恢复力并开始振荡。学生可以对所涉及的现象进行许多不同的测量，并解决与浸入分层流体中的宏观物体的行为相关的重要物理问题。尽管它很简单，但该实验允许介绍与大气和恒星物理学相关的各种理论概念，并为学生提供熟悉一个简单系统的机会，该系统可以作为模型来理解复杂现象，例如布伦特的振荡– 可见光频率和内部重力波在分层介质中的传播。