James Kakalios, a physics professor at the University of Minnesota, has written a neat opinion piece in the NY Times entitled "A Nobel for the Sandman" (Times Select subscription required to read the whole article). As those of you who have seen the new Spider-man movie know (What?! You didn't rush out to see it on opening night?!), the arch-villain that Spider-man faces is the Sandman. Not surprisingly, the Sandman is made of sand. And the computer graphics in the movie are great: the Sandman emerges from a pile of sand and dissolves away into a dust storm in a very realistic way.
James Kakalios observes that the movie "...often correctly display the fascinating properties of granular materials." In particular,
When Sandman changes his torso into a lightly packed state, Spider-Man’s ... blows futilely pass through Marko. Sandman then hardens the grains in his own hands into a rigid, close-packed state to strike Spider-Man with fists as hard as rocks.
Apparently scientists have done extensive studies of the properties of different packings of granular material. Isaac Newton may have used these studies for financial gain from his apple orchards:
For example, random pouring [of apples] fills an apple barrel to the rim, but inefficiently. Mechanical vibrations cause the apples to adjust their positions, filling open gaps and moving closer together. Barrels topped off at the orchard are thus only partly filled when they arrive at the market.
So Newton apparently used his insights for more than explaining why the moon falls just like an apple!
Fascinating things happen when you have grains of different sizes:
If you put both large and small beads in a cylinder, tip it on its side and rotate it around its horizontal axis, the contents will spontaneously segregate into alternating bands of large and small beads, like rings on a finger.
James Kakalios is the author of a book with the fascinating title of "The Physics of Superheroes"! One reviewer gives five stars with a review titled "Why can't all physics professors be like this?" I've got to put this book on my reading list!