VIS – co – e – LAS – tic
“Viscoelastic” is a term used by physicists to describe materials that behave in two different ways: a fluid (viscous) and a solid (elastic). Viscous materials are fluids like water, motor oil, or honey. Viscous substances have a great capacity to absorb energy. Amusement parks use water to safely slow down rides after a drop. This video shows a 131-foot drop on “Pilgrim’s Plunge” a new water ride at Holiday World in Santa Claus, Indiana. Will Koch is the president of Holiday World; he gets to ride with The Big Guy.
To physicists, “elastic” means rigid. Billiard balls or ball bearings are classic examples of elastic objects. Elastic substances efficiently transfer energy in a collision; they obey Newton’s third law. This great little video shows a bunch of different elastic collisions with a toy called Newton’s Cradle:
Viscoelastic substances behave both ways. If you interact with them quickly, they behave like a solid; if you interact with them gently, they behave like a fluid. This Spanish video shows a television audience playing with a pool of corn starch and water. Note: that’s a concrete mixer in the background; it takes a lot of corn starch!
Here’s a Mythbusters segment showing the same thing.
The question for today’s article: is our musculoskeletal structure fluid (viscous), solid (elastic), or both (viscoelastic)?
As noted earlier, liquid water is primarily fluid, but can be quite rigid if you hit it the wrong way: a belly flop! Audrey Tautou in “Amélie” collects smooth flat stones; this clip shows how she uses them:
One example you will be able to do at your home or at a bed store: if you gently push on a Tempurpedic or other “memory foam” mattress, you hand will sink into the structure (fluid!). If you slap the surface of a Tempurpedic mattress, you will leave no impression (solid!). If you do this in a store, please tell the bed salesman what you’re doing before you slap the mattress. You won’t hurt the mattress, but you may startle the salesman.
Are we visco? Are we elastic? We’re both: we’re viscoelastic!
If you have a 5-year-old who has been awake for too many hours to watch Fourth of July fireworks, he will be very fluid-like when you carry him home.
On the flip side, a racer poised in the starting blocks of the Olympic finals of the 100 Meter dash will be very rigid. He’s ready to push his body with as much force as is humanly possible.
This video shows a T’ai Chi “push hands” practice. The exercise starts with both students being very fluid and suddenly becoming very rigid. You’re welcome to watch the whole video, but you’ll get the point if you watch the first minute or so.
Our body’s tensegrity structure makes all this possible: when the lines of tension are relatively relaxed, the structure is fluid; when the tension is increased, the structure becomes rigid. Tensegrity gives us not only a vast repertoire of movement but the means to vary the fluidity of each of those movements. Judson Laipply demonstrates this in his famous “Evolution of Dance” video:
The goal is not to be as fluid as possible all the time; the goal is to have the appropriate amount of fluidity/rigidity for whatever you’re doing.
When we’re startled by a loud noise, we instantly crank up our structural tensions in a “fight or flight” reflex. Body/mind classes train us to do the opposite: lowering the tensions to restore a sense of flow and fluidity to the body. A goal of all body/mind disciplines is to be able to rapidly identify and eliminate superfluous stresses in our body at any point during the day.
Simply realizing that we are viscoelastic — that our bodies can be fluid or rigid moment by moment — can instantly alter how we hold and move our bodies.
I appreciate scientists, but they often pick words too complicated for their own good. A concept like “viscoelastic” is darn useful for each of us to pronounce, contemplate, and explore.
VIS – co – e – LAS – tic