Why hourglasses tick

The beads flowed smoothly only when passing through a hole between 2 and 12 times the size of the beads. For particles that are large relative to the hole, the flow halts briefly as the particles repeatedly form an arch that blocks the flow; when the arch collapses, the flow resumes. This was already known. But for smaller particles, the team, headed by Xiao-lun Wu, discovered the previously unknown ticking. Abstract Authors References. Abstract We have found experimentally that the flow of sand in an hour glass is oscillatory in a certain range of parameters.

Issue Vol. Authorization Required. Log In. Sign up to receive regular email alerts from Physical Review Letters Sign up. Journal: Phys. A Phys. B Phys. C Phys. D Phys. This is all well and good, but you might be wondering, so what? After all, why should we care whether sand flows evenly in an hourglass or not? Is this study just a case of scientists with too much time on their hands? Not at all. These findings are important, and not just for hourglass makers.

Many industrial activities, from mixing cement to manufacturing certain drugs, depend on carefully measuring the flow of fine powders. Studying the hourglass's ticks might help ensure you get exactly the right dosage the next time you fill a prescription.

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