Tin Cans + Bucket of Sand = New Science

Education Science
Tin Cans + Bucket of Sand = New Science

Physicists whose work requires thousands or millions of dollars of apparatus may be chagrined and/or delighted to learn of a new and startlingly counterintuitive effect discovered, by Raphaël Clément and co-workers at France’s Université Paris Diderot, using equipment that is quite literally sandbox-simple. Besides the doing-a-lot-with-a-little angle, their discovery makes for a potentially lucrative bar bet:

If you take two empty cans, one closed on the bottom and the other open (i.e. a tube), and turn them upside down, which will be harder to push into a bucket of sand? If, reasoning by analogy to liquids, you (like most people), said the closed one…well, you can sort of guess where this is heading: A closed can is, in fact, easier to push into a bed of sand than an open tube. Given the usual fine print. Adrian Cho explains over at ScienceNOW:

[T]he air trapped in the closed-ended cylinder affects the sand in a dramatic way, the researchers argue. Ordinarily, still sand acts somewhat like a solid. But if the air around the sand grains moves quickly enough, the sand will flow like a fluid, as physicists and engineers have long known. And when the closed-ended cylinder sinks into the sand, the air trapped in it rushes out from beneath the cylinder’s rim, fluidizing the sand at that point and making it easier for the stuff to get out of the can’s way. The sand has to be relatively densely packed, and the can must drop quickly. If the researchers slowly added weight to the can, the air seeped away gradually and the can descended no farther than the tube.

The paper is reportedly in press at Physical Review Letters, but seeing is believing. Try it yourself! Or, as a last resort, I suppose you could just watch the video.

10 thoughts on “Tin Cans + Bucket of Sand = New Science

  1. Ross William Drew says:

    is there a mistake in here? “you (like most people), said the closed one” … “A closed can is, in fact, easier to push into a bed of sand”, this would suggest that the findings aren’t shocking at all.

    1. Matt Richardson says:

      Most people would guess that the closed one is harder to push into the sand, but it is actually easier to push into the sand than the open one. At least that’s how I read it.

    2. Peter Oxley says:

      “… which will be harder to push into a bucket of sand? … if you … said the closed one …”

  2. Matt Richardson says:

    That’s really interesting! Just when you think you understand the simple things, someone comes along and shows that the world doesn’t always work the way you assume it does.

  3. Joe the Plumber's neighbor says:

    If this is a new effect to you, you nerds need to get out to the beach more, play in the sand and surf, act like children again. Try this in wet sand and see what happens.

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and makezine.com. My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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