Yogurt Jets


Imagine the following scenario: after having had the first bite of a “solid” yogurt one drops it on the ground from the typical height of a table (see Figure) . Upon impact something unexpected occurs : a thin jet of yogurt is ejected from the container following an upward vertical trajectory although one may have anticipated a more classical splash as obtained when dropping a plastic glass filled with water in the same operating conditions.

The question of why such a jet is produced is well known from explosive experts. Indeed the energy accumulated during the yogurt free fall is transmitted to the lower part of the hole made by the spoon in the yogurt that in turn gains a large speed towards the ceiling. This is known as a hollow charge.

The overall goal of the study is to quantify such a jet and model its behavior

This project may be divided in two separated and independent assignments :

1 – Design of a “yogurt dropping” apparatus. The free fall and jet will be characterized with a high speed camera that records movies similar to the one shown in the Figure above.

2 – Fabrication of “yogurts for scientists”. The yogurt itself will be made of Carbopol™ commonly used as an industry gel. The hole in the gel will be molded using a 3D printer.

Advisor: Dr. Pierre-Thomas Brun, LFMI