HERO'S FOUNTAIN:   A CUTE DEMONSTRATION OF THE POWER OF HYDROSTATIC PRESSURE

Hero, circa 200BC, wanted to produce a self-driven fountain in his garden.  He concocted an underground chamber that uses hydrostatic pressure of the pond itself to generate a fountain.  This is shown by a demonstration using a sawed off pop bottle attached to a lower pop bottle by a housing.  Two tubes emanate from the housing as illustrated.

The principle is that the hydrostatic pressure of the pond plus the tube below going into the lower reservoir (with height Ht) can lift a water column Hc with length equal to its own height (i.e. Hc ~ Ht).  Since air density is 1/1000 that of water, provided the fountain tube is less tall above the surface that the depth Ht, some water should come out the top.

1. Have some water covering the lower tube inlet
2. Fill the top tube (the "pond") about half way up and watch the fountain go (may need video camera and auxiliary illumination for large classroom).
3. First use a separate unit with the air space below the pond filled up to show that "it doesn't work" (and that the lecturer doesn't know what he/she is doing).

©2000.  John Hart, University of Colorado