Exhibits In Extreme Close Up is a series in which we examine pieces of our exhibits using a scanning electron microscope.

Dance Of Opposites is sometimes called a wallflower exhibit. It doesn't get as much attention as some of our other exhibits but it's been around forever, and what it does it does well. It's a stately old gentleman of the exhibit floor.

After placing small chunks of styrofoam between two metal plates, our visitors rub a plastic paddle on a wool cloth. When the paddle is placed near the upper plate the pieces of styrofoam begin "dancing" up and down.

The same static cling that makes freshly dried bed sheets stick together is also what's causing the chips of styrofoam to bounce up and down. With each bounce, the chips soak electrons out of the lower plate and deposit them on the upper plate.

All of the styrofoam for this exhibit comes from various packages we receive in the mail. Staff members dump their unwanted packing peanuts in a designated cardboard box and this informal system keeps the exhibit well stocked throughout the year. 

Dance Of Opposites has a tendency to make a mess of itself. By the afternoon there's usually a dusting of white smithereens all over the floor around the exhibit. Sometimes a well-meaning visitor will mistake the styrofoam for garbage and will meticulously gather it all up and throw it away, leaving the exhibit spotless but unusable. During a recent round of exhibit refurbishment we decided to try and solve this "Good Samaritan" problem.

These days we do a lot of our exhibit design work using 3D CAD software. Vicente Oropeza, the Exhibit Technician who made the recent updates to Dance Of Opposites, began by creating a virtual model of the exhibit.

In software, it's easy to explore several variations of the exhibit design until you find one that looks promising. Vicente ended up designing a deeper, wider moat for capturing the styrofoam chips. He also changed how the label was attached and spruced up a few other details on the exhibit.

And here's the exhibit after its face lift (notice no chips on the floor!).

At 50x magnification, a piece of styrofoam looks like an intricate sponge. Notice the small pieces of black sand that got on this sample.

Zooming in a little closer it becomes clear that this stuff is mostly air. Styrofoam is what's known as a closed-cell foam, a densely packed volume of sealed cavities. 

At 250x magnification we can see into one of these cavities on the styrofoam's surface, with walls made of exceedingly thin polymer sheeting.

At 1,000x we can examine the miniscule rumple of this polystyrene membrane.

From the archives:

Back in the 80s we would film exhibit maintenance videos to help us archive and take care of the exhibits collection. Below we see a clip covering the original version of Dance of Opposites, back when it was called Pluses and Minuses and had a bright yellow housing. In its younger days this exhibit included two paddles which were rubbed on what appear to be actual pillows sandwiched inside of wooden frames. OG Exhibit Developer Richard Gagnan explains the exhibit...