Sand Images

Scientists working on grainy materials frequently call them "another state of matter". On one hand they have properties typical for liquids: (These materials behave on one hand like water): they adopt the shape of the container, like the salt in the salt shaker. Collisions with granular material are always inelastic, like a long jumper landing in a sandbox.

On the other hand, they show a high coefficient of friction, like solids. In some respects their properties differ from those of liquids - e.g. they assume also their own shapes. Sand dunes have moon-like, wave-like or even stark-like shapes. Mountains seen from airplanes remind us that volcanic lava is not a liquid, but a grainy material.

Granular media (also in flow) can behave like liquids, even waves can propagate in them. Snow, sand, mud are typical media in which avalanches are possible – once the static friction inside them is overcome, even locally, nothing can stop their movement. Avalanches in particular have been studied thoroughly for the sake of skiers' security. Observing the variety of forms of sand pictures is really relaxing.