I once read an article that captivated me. As I was reading it, all I could think of was the children in my classes over the years who play with sand. And I thought of all of the times we’ve had to defend the practice of play as well as playing in the sand throughout the years. This article, Riddles In The Sand was written in 1996. Maybe more research has been done on sand. Maybe scientists and physicists understand how sand works now, at least more than they did in 1996. But as I read it, I was reminded that children are scientists. Children are physicists. Children are engineers. Every day, across the world, children are involved in theorizing, in planning, in trying out theories, and in finding ‘proof’ for their discoveries.
I was captivated, am still captivated, by the article, by the medium of sand, and by the idea that children are scientists. That is the purpose of this blog post. I wanted to put pictures to the words. I wanted to give credence to children and their play. I wanted to show that just as physicists and engineers theorize and experiment with materials, the idea to experiment, to theorize, begins in childhood. It begins with play.
Riddles in the Sand
Physicists completely understand a solitary grain of sand. Why, then, are they at a complete loss to explain a mere handful of the stuff?
“That not even a physicist can explain why sand behaves the way it does seems astonishing. Sand is neither invisibly small nor impossibly distant; observing it requires neither particle accelerators nor orbiting telescopes. The interactions of grains of sand are entirely governed by the same Newtonian laws that describe the motion of a bouncing ball or the orbit of Earth about the sun. The odd behavior of a layer of sand bounced up and down on a tray should, in principle be entirely knowable and entirely predictable. Why, then, can’t Behringer [the physicist mentioned in the article] simply take a bunch of equations describing the motion of all of the individual grains, put them in a very large computer, and wait–for years, if necessary–until it spits out a prediction?” (p 2/9)
“Because the language of physics does not contain a vocabulary for granularity, engineers must treat granular material as either a liquid or a solid. These approximations work most of the time, but occasionally they lead to disaster….when the grains come to rest against one another they form intricate, quasi-self-supporting structures. That is why adding more grains to the top of a silo often does not increase the pressure delivered to the bottom at all, but rather increases pressure outward agains the sides of the silo.” (p 3/9)
“Engineers who design buildings and roads, on the other hand, assume that under stress the supporting (and granular) soil will behave like a deforming solid, much the way plastic does. Once again, this convenient approximation occasionally leads to disasters.” (p. 3/9)
“…if engineers understood the physics of soil better, these disasters might have been avoided.” (p. 3/9)
“If you really want to describe what sand is doing in any given situation, you have to know which modes are dominant and which sets of equations you’ll need to employ…. (p. 7/9)
“You just have to recognize that not everything you do is going to shake loose major pieces of knowledge… But collectively, and on rare occasions, experiments will come along and make a significant impact. It’s like looking at a distribution of avalanches- you have a lot of little ones and, every once in a while, a big one.” (p. 9/9)