If you’ve ever poured resin or concrete into a form, you’ll know that tapping the mold helps force our air bubbles from the finished product. A new experiment in Spain helps illustrate exactly why that is.
Researchers at the University of Navarra ran and filmed a pretty cool physics experiment. They placed 25,000 dice — each half a centimeter wide — in a large plastic cylinder, and then shook the daylights out of them. In the end, this caused the thousands of unordered dice to line up in perfect concentric circles.
Shaken, not stirred
This experiment showcases a property known as ‘maximum density’. If you pour some sand in a container, for example, small gaps will remain between individual grains of sand. Since they’re randomly ordered, it’s statistically inevitable for such spaces to exist.
If you were to tap the container, mechanical energy will be transferred to the sand. This makes them shift ever-so-slightly, which eventually causes some of them to fall into the gaps, closing them up. In theory, if you take this to its practical limit and there are as few gaps as possible between the sand grains, you reach its ‘maximum density’ — since density is an object’s mass over its volume (and empty space is just volume).
But the old motto of ‘show not tell’ stuck around for a reason, and Diego Maza along with his colleagues at the University of Navarra did just that. They also used some mechanical help to speed up this process.
First, the science bit, then, the video. The team ran the experiment several times, using different mixes of speeds that the cylinder was rotated at and different numbers of rotation cycles. Rotating the cylinder above 0.5 g (1 g is the acceleration produced by gravity, i.e. the one at which things fall down) was most effective at ordering the dice. Maximum density was reached about around 10,000 rotations, the team adds.
It might seem like a complete waste of time, but experiments such as this could go a long way in environments that don’t have natural gravity, such as on the International Space Station. It is also very good material for any geologists studying deposition mechanics, as the way these dice move here is very similar to how particles of sediment behave in nature.
But, without any more ado, here’s the time-lapse video of the dice arranging themselves: