We rode Belle Isle’s giant slide with a physicist

Dozens of people lined up at the Belle Isle giant slide on Friday to find out whether riding it would actually, to quote Gmac Cash, feel like jumping off a building. Standing near the front of the line, Bill Llope, a physics professor at Wayne State University, was almost vibrating with excitement. Not at the prospect of catching air; he was on the verge of figuring out exactly how the thing works.

For a long time, no one gave much thought to the physics of the giant slide. It was a highlight for kids on family outings to Belle Isle, and that’s all.

Then, two summers ago, the physics of the slide became a cross between a national joke and a litigation nightmare. Overnight, seemingly everyone had winced their way through footage of bodies bouncing down the slide at improbable angles. The Today Show was shocked . Lizzo, who grew up with a tamer version of the slide, said she’d consider riding it in knee pads and a helmet .

Last month, with the slide set to reopen, Outlier Media asked Llope what the heck happened. We thought a quote would be nice for this story, but we got more than we bargained for when he agreed to hop into a burlap sack himself and take his maiden voyage down this city treasure.

To Llope, the giant slide is a sinusoid on an inclined plane with five cycles.

To put it another way, this is a large, wavy slide with the potential to do some serious damage if it gets too slippery.

Problems only start when riders get going fast enough to catch air off the bumps.

“As soon as you get going too fast, you’re in deep trouble: You’ve been launched,” Llope said, gesturing to the hand-drawn diagrams he’d prepared to demonstrate the forces involved. “And now it’s only going to get worse, because … now you’re in freefall, and the friction goes to zero. And your speed is increasing much, much more than it would have had you slid” along the surface of the slide.

“It does indeed have everything to do with friction.”

And that’s it, in a nutshell. In 2022, park rangers for the Michigan Department of Natural Resources, which manages Belle Isle Park and the giant slide, did in fact blame the dangerous speeds on a fresh coat of wax — that is, not enough friction.

Except the story doesn’t end there. Because Llope got curious. The abstract diagrams he presented to Outlier over a one-hour Zoom call were a start, but they couldn’t tell us exactly how fast people were going in 2022 when they thudded to the bottom of the slide, or how hard they thudded. The diagrams couldn’t tell us what the coefficient of friction was in 2022, or what it would have to be to deliver Llope’s ideal ride: plenty of speed, just a bit of airtime.

To get that information, he’d have to build a simulation of the slide, and that’s what he did. It took a weekend and about 1,000 lines of computer code to build the program. When he was done, you could enter an amount of friction and get back an object’s precise speed once it reached the bottom of the simulated slide.

“This black line is the person’s trajectory,” he said, demonstrating an almost friction-free version of the model earlier this month. “You see that the person is sliding, sliding, sliding, and then, slide, whee, crash! Slide, whee, crash! Like four crashes!”

Large slides aren’t Llope’s usual area of inquiry. He spends more time thinking about the quark-gluon plasma, which has a Wikipedia page and we’ll leave it at that. His idea of summer fun is a stint at a particle accelerator in New York, where for decades he’s helped smash subatomic particles together at the speed of light to simulate and study the universe as it was microseconds after the Big Bang.

But he’s also a teacher tasked with giving students at Wayne State University an introduction to the basic laws of physics. Objects in motion stay in motion absent another force, and the same can be said for Llope’s curiosity and zeal for explaining how the universe works.

He’s sometimes hired by attorneys to explain the physics of, for instance, an object falling on someone at work — a job he was apparently born for.

“He is a physicist to his core,” said Catherine Llope, his daughter and a senior engineering major at Wayne State. “Any time I ask a question, it’s always a two-hour sit-down, like, ‘Let me tell you what the particles are doing.’”

Llope hoped that his model would accurately predict how an object would move on the slide, but that wasn’t possible without its exact dimensions, which he didn’t have.

As he waited in line on Friday morning, he seemed more excited about collecting new data than riding the slide. He planned to count the steps to the top of the slide to confirm its height. That would be easy, but he expected to have a harder time measuring the angle of the slide at two points, which seemed to require climbing partway up the slide from the bottom.

The crowd around him let out a groan when the first riders pushed off and promptly ground to a halt. “Are you kidding me?” someone yelled.

Belle Isle staff seemed ready to capitalize on the slide’s 15 minutes of internet fame — and to defuse its reputation as a public health menace. They were ready on Friday morning with two bounce houses, lawn games and giant slide t-shirts for sale. If their goal was a big party and an underwhelming sliding experience, they achieved it.

The coefficient of friction appeared to be “more than 0.2,” was Llope’s early guess. “It’s almost unusably sticky.”

Riders did seem to be picking up a bit more speed by the time he reached the front of the line. “People are actually making it to the end of the sinusoid!” he exclaimed.

Llope climbed the 91 steps to the top, stepped into the burlap sack provided by a park ranger, and activated an app on his phone that would collect physics data from the ride down. He made it almost to the bottom, quickly hopped out of the sack, and scrambled back up the slide as he pulled a level out of his pocket to take angle measurements at a couple of points along the slide.

“No taking photos on the slide!” someone yelled as he got the data he needed and confused sliders peered down from the top.

“From a scientific perspective, that’s when I felt the most badass,” Llope said later. “I had to do it for science.”

Llope is still hoping to refine the model by gathering more data. Once he’s satisfied, he plans to write up the technical details of his work and maybe even submit it to a physics journal. Like Detroiters on the giant slide, science advances slowly until it doesn’t.

We rode Belle Isle’s giant slide with a physicist · Outlier Media