|MadSci Network: Physics|
Sorry, but I think you're going to be disappointed on this one. Particulate systems such as hourglasses are very hard to predict. Although the motion of each individual particle is simple, and governed by Newton's laws of motion, when you add a whole lot of them together the motion becomes unpredictable. It's a great example of a complex system built from the behaviour of very simple parts. In engineering applications of particle technology we rely extensively on experience, computer intensive simulations and some engineering common sense. About the only thing you could say about your system is that since the forces encouraging the sand to move downward are less, the hourglass will take longer to drain than it would on earth. However, it might not even drain at all, the sand may remain stuck in the top chamber if the gravity forces are not enough to overcome friction. It also depends on the kind of sand used and the design of the hourglass. So, the only way to answer your question, in my opinion, is to actually do the experiment on the moon, or, more cheaply, to run a discrete particle simulation on a computer. An example of this kind of simulation work (actually these guys simulated something very like an hourglass) is "Simulation of Descending Particles in Water by the Distinct Element Method": K.Asakura, S.Harada, T.Funayama and I.Nakajima, Powder Technology 94 (1997) pp195-200 Cheers, Graeme
Try the links in the MadSci Library for more information on Physics.