Snake hips, good core strength and a willingness to look slightly ridiculous all come in helpful for those wishing to master the art of hula hooping. Now scientists have concluded that an hourglass figure may also be advantageous.
The study, involving gyrating robotic figures of various dimensions, suggests a narrow waist and large hips are optimal for keeping a hoop spinning in a stable position. But those with less curvy physiques may be able to compensate by making larger hip movements at a faster pace, the analysis concluded.
“You need to throw the hoop sufficiently fast as your initial condition. You also need sufficient curvature of the body. You also need a sufficiently sloped body,” said Olivia Pomerenk, a PhD candidate at New York University and co-author of the analysis.
The paper is the culmination of about five years of research by applied mathematicians at New York University, who began investigating because “there’s such a fundamental question about how the hoop actually stays up”.
“It seems as though your body is only pushing the hoop outwards, you can’t immediately understand what is holding it up,” said Pomerenk, who joined the project more recently. “It’s a seemingly simple system, but actually involves quite intricate maths.”
To tackle this mystery, the researchers 3D printed a series of plastic shapes: cylinders, cones and hourglass-like figures (hyperboloids) with varying slopes and curvatures. “A cylinder has no slope and no curvature. A cone has slope but no curvature – it is angled but it’s a flat line,” said Pomerenk. An hourglass has both slope and curvature.
The shapes were coated in rubber, mounted on gyrating poles and recorded using high-speed cameras as hoops were whirled around them.
The experiments suggest that three crucial conditions need to be met for a reliable hoop spin to be maintained. First, the hoop needs to be launched with enough vigour.
“A first frustration faced by novices is how to launch the hoop to initiate twirling, and our experiments similarly involve false starts in which the hoop loses contact with the body if the launch speed is low,” the paper says.
The best launch strategy involves beginning with both the hoop and the body centre displaced to the same side, the paper suggests.
The analysis, published in the Proceedings of the National Academy of Sciences, found that below a critical waist/hip ratio and when the waist was too angular, rather than following a smooth curve, it was impossible to attain a stable spin.
In real life, hula hooping should be possible for most people, Pomerenk said, because in general “you don’t have humans with no slope or curvature”. Those with less optimal body shapes may need to gyrate more vigorously to keep the hoop spinning. Another option is using a hoop with a larger circumference, the paper suggests. The weight of the hoop appeared to be less important in determining its dynamics.
According to the authors, the findings may have useful applications in how to harvest energy from vibrating objects or manipulate objects using rotational forces instead of gripping them.
