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 25 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 this edition of HowStuffWorks,
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 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
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
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.
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
Photo courtesy Splashtacular,
water slide rockets you around a series of sharp
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.
Bits and Pieces
A small water slide, the
sort you might find in somebody's backyard, has a very simple
construction. It's a single piece of smooth fiberglass
material, cast in the shape of a slide, supported by a metal
Most water park slides have a similar structure, but on a
much larger scale. Obviously, it's not feasible to use a
single piece of fiberglass for a giant, curving slide. Water
park slides are formed from dozens of fiberglass
segments fastened together with heavy-duty bolts.
Typically, the individual segments fit together like sections
of a toy race track.
Each segment has one end with a raised lip and one
end with a sunken step. When you fit two segments
together, the lip of segment A rests on the step of segment B.
This ensures that the segments hold together, with a smooth
seam between them. Ideally, the slide feels like a single unit
to the rider. Slides typically use completely enclosed
tubes for the sharpest turns, to make sure everyone stays
These segments rest on a framework of steel girders.
The girders may be positioned directly below the slide, or
they may sit adjacent to the slide, supporting it with sturdy
Photo courtesy Splashtacular,
This water slide is
built around several steel columns, which hold up the
fiberglass segments with strong cantilever
parks generally buy new slides from an outside manufacturer.
The manufacturer designs the slide and builds all of the
individual pieces. The water park hires a local contractor to
take these pieces and put the whole thing together according
to the manufacturer's directions. It's just like building a
toy race track or model train, but on a massive scale.
In this serpentine water slide, the sharpest
curves are completely enclosed, so riders won't go
flying off into
The actual slide structure is only half of the ride, of
course. In order to zip down the slide, you need a constant
stream of water. In the next section, we'll look at the
pumping system that generates this stream.
Slip Slidin' Away
As we've seen, a water
slide needs a constant stream of water to reduce
friction between you and the fiberglass surface. To
maintain this stream, the water park has to get a supply of
water to the top of the slide. Most water slides do this with
a pump, housed in a building near the base of the
slide. In the standard design, the pump motor turns a drive
shaft, which is attached to a propeller. The spinning
propeller drives water forward, in the same way an airplane
propeller moves air particles.
The pump draws water from a collection sump,
typically the pool at the base of the slide, and pushes it up
through a narrow pipe to the top of the slide. In this way,
the water running down the slide is constantly recycled. In
some parks, the water is cycled through several connected
pools before it is pumped back up to the top of a slide.
One of the pump rooms at Wet
'n Wild Emerald Pointe. In these rooms, pumps draw
water in from a collecting pool, pass it through a
filtering and chlorinating system and pump it out to
slides and other rides in the park.
In a typical set-up, the water line has a check valve, also
called a one-way valve, positioned between the pump and
the top of the slide. Water can only flow upward through this
valve. This makes things easier for the water park
facilitators. When they shut off the pump at night, all of the
water from the check valve to the top of the slide sits in the
pipe. When they turn the pump on again in the morning, they
don't have to wait for the pipes to refill; the water starts
To keep everything sanitary, the water in the
collection pool is also pumped through a strainer and a filter
system. The typical filter is a large container filled
with sand, which sits on top of a layer of gravel. Water is
pumped from the top of the container to the bottom, through
the sand and gravel layers. The sharp edges of the fine sand
particles trap the bits of dirt in the passing water.
At night, the park managers reverse the flow of water
through the filter. As water moves up through the sand, it
dislodges the bits of dirt, cleaning the filter. This
backwash is pumped out to the sewer line.
In a typical collecting pool, all of the water is passed
through the filter several times a day. Any swimming pool is
constantly losing water -- through filtering, evaporation and
people carrying water away in their swim suits. To keep the
pools filled, the park has to pump in more water, either from
a well or the city line.
Water slides continue to advance at a breakneck pace. One
of the most interesting advancements on the horizon is the
so-called "water coaster." In the past, water slides
have been gravity-driven rides; the water doesn't do much more
than help you along on your descent. But some newer designs
actually use water to push you uphill. In these rides, the
pump system drives high-pressure water to several points along
the slide. When the slide dips, the water jets propel you up
the next hill. With this element, designers can make slides
that carry you in a complete circle, like a roller coaster.
It's really amazing what you can do with only water, plastic,
fiberglass and gravity.
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