In the amusement park industry, the roller coaster is king. But during the hot summer months, these classic attractions get some tough competition from water slides. In the past 30 years, the world of water slides has exploded. Water parks boast slides with dozens of loops, top speeds and exhilarating, 100-foot drops. A water slide is like a wet roller coaster with no seat and no safety harness.
 In the past 25 years, water parks like Wet 'n Wild Emerald Pointe in Greensboro, NC, have sprung up all over the world. See more water slide pictures. |
In this article, we'll peek behind the scenes to find out what's involved in operating a water slide. We'll also see how the pieces of a water slide fit together and see what keeps you from flying off into the air as you whip around corners.
The Physics of Falling
At its most basic level, a water slide is a relatively tame roller coaster with no track and no car. If you've read How Roller Coasters Work, then you know that coaster cars are driven by gravity. At the beginning of the ride, the coaster car is pulled up the lift hill. As the coaster rises higher in the air, its potential energy, or energy of position, increases. Simply put, it has farther to fall. When the coaster is released at the top of the hill, gravity pulls it down the track, converting potential energy to kinetic energy, or energy of motion.
 The simplest sort of water slide is a small, curved hill that is lubricated by a stream of water. |
Water slides work on exactly the same principle. But instead of a lift hill, you have a stairway. Climbing the stairs builds up a certain amount of potential energy, which turns into kinetic energy as you head down the slide. A taller slide has more potential energy to work with than a shorter slide.
On a water slide, your body, sometimes combined with a mat or raft, takes the place of the roller-coaster car. Coaster cars have wheels that roll along the track. This reduces the friction between the car and the track, so the car can keep moving. Water slides have a constant stream of water flowing from the top to the bottom. The water lubricates the slide to reduce the friction between the slide and your body.
 When you climb to the top of this towering water slide, you've built up a lot of potential energy for your trip down the slope. |
Apart from total height, the main difference between particular water slides is the way they put the potential energy to work. This is determined by the shape of the slide.
The slide applies a force working against gravity. The balance of these two forces depends on the angle of the slide. When you are sliding along on a nearly level slope, gravity pulls you directly into the slide, and the slide pushes you upward. The upward force of the slide pushes nearly opposite the downward force of gravity, slowing your downward acceleration. When the slope drops sharply, gravity is still pulling you straight down, but the slanted slide is no longer pushing you straight up; it's pushing you at an angle between upward and forward. Since the slide isn't working directly against gravity, you accelerate downward more rapidly.
Speed slides and sled slides focus only on these up-and-down forces. On a speed slide, you plummet straight down a steep slope and launch into an exit flume, a long canal of water that slows you down gradually. In a sled slide (also called a toboggan slide), you glide over a series of bumps and dips. In both of these slide designs, you move forward in a straight line.
 A speed slide, like this one at Wet 'n Wild Emerald Pointe, has a dramatic drop that launches you into a long exit flume. |
Serpentine slides add something new to the mix: curves. The slide snakes around on its way to the bottom, whipping you in different directions all the while. In this sort of ride, the slide structure is not only working against the force of gravity, it's working against your own inertia. When you speed toward a curve, your body naturally wants to keep going forward. If the slide were flat, you would be launched into the air at the first sharp turn. The slide has to curve up at these turns to keep you on the ride.
 Photo courtesy Splashtacular, Inc. This serpentine water slide rockets you around a series of sharp turns. |
When you hit these curves, you feel a strong force acting on your body. This is the slide accelerating you -- changing your forward velocity -- so you move in a different direction. (See How Roller Coasters Work to find out more about these forces.)
For everything to work correctly in a water slide, you need a sturdy, smooth surface to glide on. In the next section, we'll look at the structural elements of a water slide.
