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How do water slides work?

Jane Lindholm
Vermont Public

How do water slides work and how are they built? Why do you have to be a certain age or height to go down a water slide? Where does the water in water parks come from? And which is easier to design and build: a water slide or a roller coaster? First we did a little research of our own at Jay Peak Pump House Water Park. (And by “research” we mean “going down the water slides.”) And to teach us more about what’s actually happening when you take your thrill ride, we talked with water slide engineers Songyi Moon and Kelly Sall at WhiteWater West.

Download our learning guides: PDF | Google Slide | Transcript

  • Designing a water slide takes a lot of math and physics! The engineers told But Why the math isn’t too complicated. What’s challenging is applying that math to the variable conditions of real life parks. 
  • Engineers have to make sure that water slides work for people of all different heights, weights and shapes.
  • The important forces are friction and gravity! When two objects come in contact with each other, they create friction. In a water park, engineers will want to make sure there’s a lot of friction on stairs to keep people from slipping. But when you’re going down a slide, there should be a lot less friction. The slide material, water, and sometimes floaty tubes or rafts will all help cut down on friction. And the downhill trajectory brings gravity into the equation.
  • When people climb up to the top of the slide they create potential energy. Kinetic energy–the energy of motion– is created when someone starts moving down the slide. 
  • If a person has enough energy they can even do a loop-de-loop upside down for a second or two without sliding backwards! 
  • Water parks use a lot of water. One park might take 900,000 gallons of water to fill up the slides and pools. The water park industry says once the park is filled, the water is usually reused so they don’t need to keep filling it up. Though they do need to replace water that is lost to splashing and evaporation. 
  • Water parks also have filtration and cleaning systems and use chemicals, like chlorine, to kill germs.
  • When a ride says “you must be this tall to ride,” part of it is how big someone is, but height is also a proxy for age. Kids have to be at a certain stage of development to intuitively hold on, brace against forces in the ride, and generally behave in a way that will keep them safe in the design of the ride. Younger kids might not know how to keep safe around a curve and could get hurt. 
Jane Lindholm is the host, executive producer and creator of But Why: A Podcast For Curious Kids. In addition to her work on our international kids show, she produces special projects for Vermont Public. Until March 2021, she was host and editor of the award-winning Vermont Public program Vermont Edition.
Melody is the Contributing Editor for But Why: A Podcast For Curious Kids and the co-author of two But Why books with Jane Lindholm.

But Why is a project of Vermont Public.

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