Social dancing had long been a staple of student life, but over the last few decades, it has seeped into curricular life, particularly with the arrival of Richard Powers to the Dance Division in 1991. Powers, himself a former engineering student at Stanford, speaks to a broad swath of the student population, making dance accessible to students across the university.
One, a Ph.D. student in Mechanical Engineering, wrote this final essay – “Pivoting is Hard” – for one of Powers’ social dance classes:
“Considering this was the second dance class I’d ever taken, it’s probably not surprising that I would find pivoting to be difficult. Spinning around your partner at breakneck speeds, holding on for dear life, is not really a skill I’ve been trained in. Pivoting, in and of itself, does not have to be hard. If both partners are engaged in spinning around each other, all the while controlling their distance, it works pretty well. However, the moment one partner decides they want to lean away a little more, the pivot turns into a flyball governor, you start slowing down, and the whole thing becomes a frantic exercise in getting back to starting position before the couple behind you slams into you at full speed.
There are a couple of ways around this. First, I’ve found that more petit partners influence the moment of inertia of the pivot considerably less. As a result, regardless of whether they are at close distances or not, the effect they have on the pivot as a whole depends only on whether they are spinning fast enough and not letting go. It’s kind of like the moon and the earth: although the moon’s gravitational pull affects the earth in minor ways, the center of gravity and the rotation remain stable. Second, with partners of similar size, distance becomes a critical issue. The closer the two are during the pivot, the less centripetal force they experience, and the easier it is for them to rotate. Further, by being closer together, the center of mass of the pair remains fairly stable, reducing the “wobble” experienced by leaning back too far. In short, the mass of the two bodies in motion controls the moment of inertia and center of gravity of the pivot. By taking this into account, the pivot can be tailored to the individual couple, which reduces the difficulty associated with it.”
Featured image: Richard Powers and partner Mirage Marrou dancing at the Google Waltz Lab. Photograph by Jason Chuang, Stanford News Service, 2012.