sinking ice cube, OK but this time not in water but in milk shake! For
this experiment as the video opposite demonstrates, it’s a miracle, it
sinks. Just wait a few minutes and another miracle - it comes back up
to the surface.
Buzzy explains :
When the ice cube goes down into the milk it is submitted to 2 forces : its own weight P and Archimedes Pa. In the previous experiment we studied that the force pa depends on volume, but that’s not all. Pa also depends on density of the liquid. In this case whipped milk is very light and loads of air bubbles are suspended in it - this gives it a frothy appearance - lowering specific gravity and consequently Archimedes force. This lowers until it becomes inferior to the weight and then it sinks.
As minutes pass by, air bubbles burst on the surface - degassing - and gradually the specific gravity of the milk reaches its initial figure.
Pa is obviously greater than P.. The ice cube gradually rises naturally to the surface.
Pa < P
Pa > P