How to create Dry Quicksand
How to create Dry Quicksand:
A 50 cm high container with a perforated bottom of 15.1 times 15.3 cm2 is about half filled with very fine sand with an average diameter of 40 mm through which we then let air flow. Before the experiments we turn off the air stream and let the sand settle.
The bed prepared in this way has a density of 897 kg/m3, determined by measuring its total mass and the filling height after decompactification. With a quartz density (SiO2) of 2200 kg/m3 this corresponds to a packing density of only 41 %.
How the experiments are done:
A hollow ‘ping-pong' ball of radius R = 2.0 cm, of which the mass can be varied by filling in bronze particles through a small hole on the top, is suspended above and just touching the surface of the sand. To release the ball without introducing vibrations, the thin rope supporting the ball is burnt and the ball instantaneously sinks into the sand.
Either the position of ball is measured as a function of time (using a light but stiff rod attached to the top), or the emergence of the jet is imaged. For this we use a high speed camera at frame-rates of 1000 Hz and 2000 Hz.
See also the web pages of the research group: