"But you also have to think about air resistance. "We know from Galileo that all objects near the surface of the Earth accelerate downward at the same rate," he says. That also makes sense in terms of what we know about physics, says Martell. "But a lighter rider-that person will get flushed and get swept up by the water and they'll eventually reach the speed of the water." "They can't break through the deep water," he says. He explains that heavier riders won't go much faster than the speed of the water itself. "More water is a very good thing if you're trying to regulate different-size riders." "I'm constantly thinking about the depth of water in every part of the ride," he says. So how does Hunter make sure the lightest riders and the heaviest riders stay safely on his slides? This makes sense if you think about it: Going around a smaller curve will not take as long as going around a bigger curve. "You want to start out with a bigger curve, because a curve with a longer radius is a smoother ride." "I'm not going to take riders into a short-radius curve right away," he says, talking about a hypothetical new slide. (Video: "I Didn't Know That: Roller Coaster Testing.") For 30 years he's tested every kind of waterslide curve-from large loops to tight corners-and how the human body reacts to each one. Hunter is the president and CEO of ProSlide Technology, a company that's designed many of the world's biggest waterslides. It's a question Rick Hunter has pondered for decades. That's one of the things that has to be figured in-how people of all body types go up the slides." But instead, you go up the sides of the slides. "Your inertia is trying to take you through the waterslide and out. "That's why the waterslide has curved sides," says Martell. (But if it did, you'd plunge over the edge of the slide.) In other words, each time you reach a curve on a serpentine slide, your body tries to keep going forward. It's called inertia, and it's the resistance your body has to changing its speed. That's true for straight sections of a slide, but on a serpentine slide-which whips riders back and forth along curves-there's something else to keep in mind. And everything that happens to you on a waterslide, it's because of the forces of gravity and friction and the force coming from the interactions between the water and the slide." "But it also pushes you along like a river. "Water acts as a lubricant between you and the slide," he says. He lists the forces acting on riders on a waterslide: gravity, of course, but also the friction between your body and the slide (or the tube you're on and the slide) and how the water interacts with the slide itself.
"And then you have some forces acting on you which cause you to accelerate, which means a change in velocity." "You start out at the top of the waterslide at rest," he explains. So we turned to some experts: the people who design water parks rides, a physicist with three small children, and two 14-year-old twins who are self-described "water park enthusiasts." (Related: "Water Park, Peru.") In the poignant coming-of-age story, 14-year-old Duncan (Liam James) escapes his complicated family life by working in a highly chlorinated summer water park, where he makes good friends and escapes his troubles by plummeting down slide after slide.Īt National Geographic, we enjoy a good waterslide (who doesn't?) but were also wondering just how they work-and how water parks use basic physics and engineering concepts to keep their 85 million annual riders safe. The waterslide even plays a starring role in the critically acclaimed summer movie The Way, Way Back, which opens this Friday. The once-simple backyard pool accessories-remember those light blue, 6-foot-tall (2-meter-tall) slides?-now have hairpin curves, exhilarating loops, and drops that span multiple stories. The Disney park is one of almost 2,000 water parks that have cropped up around the world in the past 30 years. Riders reach speeds of up to 60 miles (90 kilometers) per hour as they plummet down a free-fall slide with fake snowbanks on each side. It's not hard to see why: The 12-story waterslide has one of the tallest and fastest drops in the world. At the top of the Summit Plummet waterslide at Walt Disney World's Blizzard Beach in Orlando, Florida-which stands some 120 feet (37 meters) above the ground-thrill seekers have been known to turn back.