Sand provides children with hours of entertainment; it is the raw stuff of fantasy sandbox kingdoms, and as it trickles through an hourglass provides a mesmerizing vision of the passage of time. Sometimes scientists make sand toys, too. One of our favorites, a tall, clear-plastic cylinder nearly filled with fine sand encasing a single large ball near its bottom, reveals some rather perculiar properties of this material. For example, can a child bring the steel ball to the top of the sand? Perhaps surprisingly, a few vertical shakes of the column will move the ball upward until it reaches the top.
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