  The lifting effect of an effervescent tablet in the water is ideal for
educational purposes, because it combines various mathematical and physical
principles. We developed a mathematical toy model for the time evolution of the
buoyancy and the weight on such a tablet. According to this model we conclude
at a mathematical formula which connects the lifting time of the tablet with
the geometrical characteristics of it. We tested this formula experimentally
and it seems to be confirmed pretty well, according to the experimental data.
