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How Roller Coasters Work
BY TOM HARRIS & CHERISE THREEWITT
If you enjoy studying physics (and who doesn't), there are few more exhilarating classrooms than roller coasters. Roller coasters are driven almost entirely by basic inertial, gravitational and centripetal forces, all manipulated in the service of a great ride. Amusement parks keep upping the ante, building faster and more complex roller coasters, but the fundamental principles at work remain basically the same.
In this article, we'll examine the principles that keep coaster cars flying around on their tracks. We'll also look at the hardware that keeps everything running, as well as the forces that make the rides so much fun.
The amusement-park industry has experienced a coaster boom of sorts in recent years. New catapult launching techniques, hanging-train designs and other technological developments have opened a world of options for designers. There are now coasters that give riders the experience of flying, and those that shoot riders down long stretches of spiraled tracks. "Fourth dimension" coasters spin or rotate seats as the ride twists, turns and free-falls. Keep reading as we loop you in on all the newest features and innovations in roller coaster.
Roller Coaster History
Roller coasters have a long, fascinating history. Roller coasters are the direct ancestors of monumental ice slides — long, steep wooden slides covered in ice, some as high as 70 feet ( meters) — that were popular in Russia in the 16th and 17th centuries. Riders shot down the slope on sleds made of wood or blocks of ice, crash-landing in a sand pile [source: Levine].
Coaster historians diverge on the exact evolution of these ice slides into actual rolling carts. The most widespread account is that a few entrepreneurial Frenchmen imported the ice slide idea to France. The warmer climate of France tended to melt the ice, so the French started building waxed slides instead, eventually adding wheels to the sleds. In 1817, the Russes a Belleville (Russian Mountains of Belleville) became the first roller coaster where the train was attached to the track (in this case, the train axle fit into a carved groove). The French continued to expand on this idea, coming up with more complex track layouts, with multiple cars and all sorts of twists and turns.
The first American roller coaster was the Mauch Chunk Switchback Railway, built in the mountains of Pennsylvania in the mid-1800s. The track, originally built to send coal to a railway, was reconfigured as a "scenic tour." For a nickel, tourists got a leisurely ride up to the top of the mountain followed by a wild, bumpy ride back down [source: Levine].
Over the next 30 years, these scenic rides continued to thrive and were joined by wooden roller coasters similar to the ones we know today. These coasters were the main attraction at popular amusement parks throughout the United States, such as Kennywood Park in Pennsylvania and
Roller Coaster Components
At first glance, a roller coaster is something like a passenger train. It consists of a series of connected cars that move on tracks. But unlike a passenger train, a roller coaster has no engine or power source of its own. For most of the ride, the train is moved by gravity and momentum. To build up this momentum, the train has to get to the top of the first hill (the lift hill) or get a powerful launch.
Chain Lift
The most traditional way most trains get to that first hill is via a long chain (or chains) running up the hill under the track that simply pulls trains to the top. The chain is fastened in a loop that is wound around a gear at the top of the hill and another gear at the bottom of the hill. The gear at the bottom of the hill is turned by a simple motor.
The motor turns the chain loop so that the chain continually moves up the hill like a long conveyer belt. The coaster cars grip onto the chain with several chain dogs, which are mounted to the underside of the rollercoaster cars. Anti-rollback dogs prevent the train cars from rolling back if the chain breaks. They're also responsible for that “clack-clack-clack" sound you hear as a coaster train ascends the lift hill. Once the train cars reach the summit, the chain dogs release and the train starts its descent down the hill.
Catapult-launch Lift
In some newer coaster designs, a catapult launch sets the train in motion. There are several sorts of catapult launches, but they all basically do the same thing. Instead of dragging the train up a hill to build up potential energy, these systems start the train off by building up a good amount of kinetic energy in a short amount of time.
One popular catapult system is the linear-induction motor. A linear-induction motor uses electromagnets to build two magnetic fields — one on the track and one on the bottom of the train — that are attracted to each other. The motor moves the magnetic field on the track, pulling the train along behind it at a high rate of speed. The main advantages of this system are its speed, efficiency, durability, precision and controllability.
Another popular system uses dozens of rotating wheels to launch the train up the lift hill. The wheels are arranged in two adjacent rows along the track. The wheels grip the bottom (or top) of the train between them, pushing the train forward.
The Brakes
Like any train, a roller coaster needs a brake system so it can stop precisely at the end of the ride or in an emergency. In many roller coasters, there are also spots along the track where the train is slowed or stopped deliberately. This can be for safety reasons, such as where the train approaches the unloading zone at the end of the ride to prevent it from colliding with another train that hasn't yet departed, or through a steep curve. Track designers may also choose to slow down the train through a certain part of the ride to help build suspense for the riders. In roller coasters, the brakes usually aren't built into the train itself; they're built into the track [source: Birket].
Roller coaster designers refer to brakes that slow down the train as "trim brakes," and brakes that stop the train are known as "block brakes." In addition to these two main categories of brakes, there are also several different types.
The most common system is called a "fin brake,'' even though the fin is on the train car and the brake is on the track. A series of clamps is positioned at the end of the track and at a few other braking points. A central computer operates a hydraulic system that closes these clamps when the train needs to stop. The clamps close in on vertical metal fins running under the train, and this friction gradually slows the train down.
"Skid brakes" are most commonly found on old roller coasters and consist of long, ceramic-coated planks that rise out of the track and exert pressure on the bottom of the train to slow or stop it. There are also "magnetic brakes," which create a magnetic field between the track and the train that forces the train to slow down. Magnetic brakes are often used to complement other brake systems.
almost completely empty. At this point, the train either comes to a stop or is sent up the lift hill for another ride.
At its most basic level, this is all a roller coaster is — a machine that uses gravity and inertia to send a train along a winding track. Next, we'll look at the various sensations you feel during a roller coaster ride, what causes them and why they're so enjoyable.
Roller Coaster Forces
In the last few sections, we looked at the forces and machinery that send roller coasters rocketing around their tracks. As the trains move over the hills, valleys and loops of the track, the forces on the riders change constantly, pulling them in all directions. But why is this rollicking movement so enjoyable (or, for some people, so nauseating)?
To understand the sensations you feel in a roller coaster, let's look at the basic forces at work on your body. Wherever you are on Earth, gravity is pulling you down toward the ground. But the force you actually notice isn't this downward pull, it's the upward pressure of the ground underneath you. The ground stops your descent to the center of the planet. It pushes up on your feet, which push up on the bones in your legs, which push up on your rib cage and so on. This is the feeling of weight. At every point on a roller coaster ride, gravity is pulling you straight down.
The other force acting on you is acceleration. When you are riding in a coaster car that is traveling at a constant speed, you only feel the downward force of gravity. But as the car speeds up or slows down, you feel pressed against your seat or the restraining bar.
You feel this force because your inertia is separate from that of the coaster car. When you ride a roller coaster, all the forces we've discussed are acting on your body in different ways.
Newton's first law of motion states that an object in motion tends to stay in motion. That is, your body will keep going at the same speed in the same direction unless some other force acts on you to change that speed or direction. When the coaster speeds up, the seat in the cart pushes you forward, accelerating your motion. When the cart slows down, your body naturally wants to keep going at its
Roller Coasters and Your Body
Your body feels acceleration in a funny way. When a coaster car is speeding up, the actual force acting on you is the seat pushing your body forward. But, because of your body's inertia, you feel a force in front of you, pushing you into the seat. You always feel the push of acceleration coming from the opposite direction of the actual force accelerating you.
This force (for simplicity's sake, we'll call it the acceleration force) feels exactly the same as the force of gravity that pulls you toward Earth. In fact, acceleration forces are measured in g-forces, where 1 g is equal to the force of acceleration due to gravity near Earth's surface (9.8 m/s2, or 32 ft/s2).
A roller coaster takes advantage of this similarity. It constantly changes its acceleration and its position to the ground, making the forces of gravity and acceleration interact in many interesting ways. When you plummet down a steep hill, gravity pulls you down while the acceleration force seems to pull you up. At a certain rate of acceleration, these opposite forces balance each other out, making you feel a sensation of weightlessness — the same sensation a skydiver feels in free fall.
If the coaster accelerates down fast enough, the upward acceleration force exceeds the downward force of gravity, making you feel like you're being pulled upward. If you're accelerating up a steep hill, the acceleration force and gravity are pulling in roughly the same direction, making you feel much heavier than normal. If you were to sit on a scale during a roller coaster ride, you would see your "weight" change from point to point on the track.
At the top of a hill on a conventional coaster, inertia may carry you up, while the coaster car has already started to follow the track down. Let go of the safety bar, and you'll actually lift up out of your
seat for an instant. Coaster enthusiasts refer to this moment of free fall as "air time." More on that next.
loop-the-loop. These structures turn the whole world upside down for a few seconds. Let's take a closer look.
Loop-the-Loops
As you go around a loop-the-loop, your inertia not only produces an exciting acceleration force, but it also keeps you in the seat when you're upside down.
A roller coaster loop-the-loop is a sort of centrifuge, just like a merry-go-round. In a merry-goround, the spinning platform pushes you out in a straight line away from the platform. The constraining bar at the edge of the merry-go-round stops you from following this path — it is constantly accelerating you toward the center of the platform.
The loop-the-loop in a roller coaster acts the same as a merry-go-round. As the train cars approach the loop, your inertial velocity is straight ahead of you. But the track keeps the coaster car, and therefore your body, from traveling along this straight path. The force of your acceleration pushes you from the coaster-car floor, and your inertia pushes you into the car floor. Your own outward inertia creates a sort of false gravity that stays fixed at the bottom of the car even when you're upside down. You need a safety harness for security, but in most loop-the-loops, you would stay in the car whether you had a harness or not.
As the cars move through the loop, the net force acting on your body is constantly changing. At the very bottom of the loop, the acceleration force is pushing you down in the same direction as gravity. Since both forces push you in the same direction, you feel especially heavy at this point. As you move straight up the loop, gravity is pulling you into your seat while the acceleration force is pushing you into the floor. You feel the gravity pulling you into your seat, but (if your eyes are still open) you can see that the ground is no longer where it should be.
Types of Roller Coasters
There are two major types of roller coasters, distinguished mainly by their track structure. The tracks of wooden roller coasters are similar to traditional railroad tracks. In most coasters, the car wheels have the same flanged design as the wheels of a train; the inner part of the wheel has a wide lip that keeps the car from rolling off the side of the track. The car also has another set of wheels (or sometimes just a safety bar) that runs underneath the track. This keeps the cars from flying up into the air.
Wooden coaster tracks are braced by wooden cross ties and diagonal support beams. The entire track structure rests on an intricate lattice of wooden or steel beams, just like the beam framework that supports a house or skyscraper.Track designers can even flip the train upside down (though this is rare in modern wooden coasters). But, because the track and support structure are so cumbersome, it is difficult to construct complex twists and turns. In wooden coasters, the exhilarating motion is mainly up and down.
Even though wood has its limits, which typically make wooden coasters slower and tamer than steel coasters, it also has advantages. Wooden coasters are designed to sway slightly as the train moves through them, which lends a unique effect that cannot be replicated with more rigid materials.
The range of motion is greatly expanded in steel roller coasters. The world of roller coasters changed radically with the introduction of tubular steel tracks in the 1950s. As the name suggests, these tracks consist of a pair of long steel tubes. These tubes are supported by a sturdy, lightweight superstructure made of slightly larger steel tubes or beams.
Tubular steel coaster wheels are typically made from polyurethane or nylon. In addition to the traditional wheels that sit right on top of the steel track, the cars have wheels that run along the bottom of the tube and wheels that run along the sides. This design keeps the car securely anchored to the track, which is absolutely essential when the train runs through the coaster's twists and turns.
The train cars in tubular steel coasters may rest on top of the track, like the wheels in a traditional wooden coaster, or they may attach to the track at the top of the car, like in a ski lift. In suspended coasters, the hanging trains swing from a pivoted joint, adding an additional side-to-side motion. In an inverted coaster, the hanging train is rigidly attached to the track, which gives the designer more precise control of how the cars move.
A tubular steel track is prefabricated in large, curved segments. The steel manufacturing process allows for a smoothly curving track that tilts the coaster train in all directions. A wooden roller coaster rattles as it rolls over the joints that connect the pieces of the wooden track. In a tubular steel coaster, the track pieces are perfectly welded together, making for an incredibly smooth ride. As any coaster enthusiast will tell you, each sensation has its own distinctive charm.
According to the Roller Coaster DataBase, there were 4,639 coasters in operation around the world in 2018 — 4,455 of them steel, 184 wooden. The RCDB identifies eight main coaster types: ● Sit-down: The traditional design, with riders sitting inside a car. ● Stand-up: Riders stand on the train's floor instead of sitting. ● Inverted: The train travels below the track instead of on top of it. It is distinct from a suspended coaster since the train is fixed to the track. ● Suspended: The train travels beneath the track, but unlike an inverted coaster, the train is fixed to a swinging arm that pivots from side to side. ● Pipeline: The track is attached to the middle of the train, instead of above or below it. ● Bobsled: Wheeled trains slide down a U-shaped tube instead of being fixed to a track. ● Flying: Riders start out in a seated position but are rotated to face the ground as the ride starts, giving the feeling of flying. ● Wing: Two seats from each car are positioned on either side of the track. The seats spin or rotate on their own axis, either freely or in a controlled motion. In 2018, there were nine Wing coasters in operation with two more under construction. This type of coaster is sometimes referred to as 4th Dimension.
Never been on a coaster before? In the next section we'll give you some advice on your first ride.
Once you've made it into the coaster car, you'll be secured by one of two basic restraint systems: a lap bar or some variation of an over-the-shoulder harness. Don't be alarmed if you're getting on a loop-the-loop coaster with a lap bar — as we explained earlier, inertia would keep you in your seat even with no restraints.
The restraint system — and everything else on a roller coaster — is completely computer-controlled. Programmable logic controllers, usually three of them, monitor every aspect of a coaster's operations. They regulate the ride's speed, ensure that trains never come too close to one another, and alert human operators to technical glitches or track obstructions. The possibility that, say, the ride would leave the station with an unsecured safety belt or that an attendant would forget to apply the coaster's brake are extremely rare. All coasters are carefully inspected on a daily basis and completely worked over during the park's off-season.
Even armed with all these facts, you'll probably still be a little nervous. Just remember that roller coasters are designed to give you a thrill and to make you feel like you're in danger, if only for a few seconds. So just sit back, relax and enjoy the ride!
