One of the things sedimentologists try to do is visualize how individual grains behave. This is important for things like sediment transport and deposition - it even plays an important role in things like quicksand. In some cases, it's helpful to scale a system down so that it may be observed in a lab room, under manageable timescales. I've been working on scaling things up to look at how individual grains interact with each other. A few thousand fluorescent BBs and a blacklight help bring out the details look pretty interesting with a long-exposure photograph.