This piece was originally published by Artists Repertory Theatre for their Fresh Eyes series. Thank you to the entire company for allowing me into their rehearsal and production process, the experience was incredible and I am honored to be able to reflect on this powerful show. La Ruta runs through Dec. 1, 2019.
Sand spreads an applied force through chains formed by neighbor grains pushing on one another. To create this image, a force is applied from above. The force chains appear bright in this model and larger forces are indicated by brighter beads. Photo credit: Karen Daniels, NCSU Physics
On the set of La Ruta, the sand encroaches from every side, a symbol of the constant, surrounding fear of daily life for the women of Juarez. “… the only thing between our beds and the desert is a thin layer of concrete.” The piles of sand in the blazing sun set the landscape, and the production’s use of sand as both a character and a set piece gives life to the desert and the monsters it hides.
Even in the field of physics, sand remains somewhat mysterious. Granular materials, such as sand, are hard to categorize; they behave like a liquid in certain ways, and like a solid in others. Sand can support objects that rest on it, but it will also move freely to fill whatever space is available. Piles of sand can support very heavy loads: we are able to walk, drive, even build on it, but sand is also delicate enough to shift in the wind, drifting around corners or slipping through cracks in a wall.
Imagine stepping down onto a small pile of sand, if you could zoom in on the sand grains under your foot, you would see that the force you apply is carried through the grains in a number of force chains. These chains are formed when grains are near enough to push on each other; one grain pushing on the next, and it in turn pushing on the next grain down the chain. We can visualize force chains in a lab by using models of sand where each sand grain is represented by a small plastic disc. These discs are made from a material that will change from opaque to clear when squeezed. By stacking many of these discs in a thin layer, we see force chains appear as a connected string of bright discs; illuminated because they are experiencing an applied force. The image above shows the chains that occur when a force is applied to the top layer of discs. The bright lines show how each grain in a chain is carrying part of the load. The structures that emerge are organic, resembling tree roots or branches. Forces split apart and sometimes rejoin later as they find a unique path through the sand grains.
Looking closely at the image, we see that forces are distributed through sand in a very uneven way. Some individual grains bear most of the pressure, while others, even the grains close by, are spared from feeling any force at all. Sand is indiscriminate in how the load is carried—unfair in some ways, certainly unequal. The women of La Ruta, grains of sand feeling forces from all sides, also bear the weight in unequal ways. Some crushed by grief, barely surviving, and others seemingly unaffected by the surrounding forces.
Another observation from the plastic sand model teaches us that moving the point where the force is applied can completely rearrange the force chains, and scramble how they connect. Grains that felt nothing before may quickly find themselves bearing the majority of the force. Subtle changes from the outside have the power to completely rearrange how it feels to be in the midst of the sand, just as is the case for the characters in La Ruta.
To close with a positive aspect of this metaphor, consider how force chains give sand its incredible strength: the ability to support any weight laid upon it. By supporting one another, and organizing themselves to share the burden, individual sand grains collectively grant sand the ability to withstand incredible pressure. Unlike other solid objects, each grain of sand maintains its identity and independence, granting the whole collective the ability to move and re-shape when given the opportunity and space to do so.
Andrew Dawes 