Have you ever wondered how roller coasters stay on their tracks and why people can hang upside down in them? It’s all a matter of physics: energy, inertia, and gravity.
A roller coaster does not have an engine to generate energy. The climb up the first hill is accomplished by a lift or cable that pulls the train up. This builds up a supply of potential energy that will be used to go down the hill as the train is pulled by gravity. Then, all of that stored energy is released as kinetic energy which is what will get the train to go up the next hill. So, as the train travels up and down hills, its motion is constantly shifting between potential and kinetic energy.
The higher the hill the coaster is coming down, the more kinetic energy is available to push the cars up the next hill, and the faster the train will go. Plus, according to Newton’s First Law of Motion, “an object in motion tends to stay in motion, unless another force acts against it.” Wind resistance or the wheels along the track are forces that work to slow down the train. So toward the end of the ride, the hills tend to be lower because the coaster has less energy to get up them.
The two major types of roller coasters are wooden and steel. Features in the wheel design prevent the cars from flipping off the track. Wooden tracks are more inflexible than steel, so usually don’t have such complex loops that might flip passengers upside down. In the 1950s tubular steel tracks were introduced. The train’s nylon or polyurethane wheels run along the top, bottom, and side of the tube, securing the train to the track while it travels through intricate loops and twists.
When you go around a turn, you feel pushed against the outside of the car. This force is centripetal force and helps keep you in your seat.
In the loop-the-loop upside down design, it’s inertia that keeps you in your seat. Inertia is the force that presses your body to the outside of the loop as the train spins around. Although gravity is pulling you toward the earth, at the very top the acceleration force is stronger than gravity and is pulling upwards, thus counteracting gravity. The loop however must be elliptical, rather than a perfect circle, otherwise the centripetal (g) force would be too strong for safety and comfort.
How do we know whether a roller coaster is safe? Engineers and designers follow industry standards and guidelines. The first “riders” are sandbags or dummies. Then engineers and park workers get to try it out. Would you want to be one of the first passengers on a new ride?
- Fun facts:
The ancestor of the roller coaster is traced to Russia in the 15th century, a gravity sled ride called Russian Mountains.
- One of the first roller coasters was in France in 1817 - Les Montagnes Russes à Belleville (Russian Mountains of Belleville) - the train axle was attached to the track by way of a carved groove.
- In 1827, the Mauch Chunk Switchback Railroad, (Summit Hill, PA) built a track 18 miles down a mountain to transport coal. In 1873, it became a scenic, albeit bumpy, pleasure ride. It remained in operation until 1938.
- La Marcus Thompson built the Switchback Railway at Coney Island, Brooklyn, NY, in 1884. He has been called the “father of gravity” and holds several patents including US Patent 310,966 (1885) for “Roller coaster structure,” and US Patent 1,102,821 (1914) for “Signaling device for racing coasters.”
- One of the first high-speed coasters was Drop-The-Dip, at Coney Island, Brooklyn, NY (1907). At this time lap restraints started to be used.
- The first tubular steel coaster was the Matterhorn Bobsleds at Disneyland, Anaheim, CA (1959).
- Knott's Berry Farm, Buena Park, CA, introduced the Corkscrew (1975), the first coaster to completely invert passengers.
- King Cobra, Kings Island, Cincinnati, OH (1984) was the first roller coaster that allowed people to stand up.
- The longest roller coaster at this time is Steel Dragon 2000, Nagashima Spa Land, Japan, at 8,133 feet/2,479 m.
- As of 2005, the tallest steel continuous circuit roller roaster is Kingda Ka at Six Flags Great Adventure, Jackson Township, NJ, 139m/456 feet. It is also the fastest at 128 mph/206 km/h. A ride lasts 50.6 seconds.
For more print resources...
Search on "Roller coasters," "Roller coasters—Design and function," "Amusement rides" or "Amusement parks" in the Library of Congress Online Catalog.
Roller coasters may be vomit- and tear-inducing thrill machines, but they’re also fascinating examples complex physics at work.
Getting a string of cars through a knot of drops, flips, rolls, and launches requires teams of mechanical engineers analyzing concepts like forces, acceleration, and energy. To get an idea of the science behind our favorite rides, we spoke to Jeffrey Rhoads, a professor at Purdue’s School of Mechanical Engineering and creator of the university’s roller coaster dynamics class.
Completing the Circuit
Let’s start with the basics. Roller coasters, like everything else, must obey the law of conservation of energy, meaning the train can only go as fast and as far as the amount of stored (potential) energy allows.
Potential energy usually comes from lifting the train up a hill with a chain or cable. As a train travels down a hill, the potential energy turns into moving (kinetic) energy; the faster the train goes, the more kinetic energy it has.
The kinetic energy turns back into potential energy as the cars ascend subsequent hills. Because the cars necessarily lose some energy through forces like friction and air drag, the highest point on a traditional coaster (think: Six Flags Magic Mountain’s Goliath or Twisted Colossus rides) is almost always the first hill. If there’s another major drop coming higher than the first, the designers add more lifts (think: the big drop at the end of Disney's Splash Mountain).
Some coasters drop further than 90 degrees, curving inward at the top of the lift hill, like on Valravn in Cedar Point. The physics at play are the same, but Rhoads says these drops can offer a more acute feeling of weightlessness.
Other coasters, like Six Flags Great Adventure’s Kingda Ka or Cedar Point’s Top Thrill Dragster, store their energy in launchers, fluid or air pressure-powered pinball plungers, or in electromagnets built into the track and cars. Launch coasters don’t require gigantic lift hills (which saves a lot of space), and offer a different kind of anticipatory thrill. “Large parks want a variety of rider experiences and launch coasters are a great way to change the feel,” says Rhoads.
Loops, Flips and Turns
Engineers generate thrill through acceleration—basically changing riders’ velocity in highly engineered, unnatural ways. Coaster engineers call upon Newton's laws of motion to get riders to feel the combined forces of gravity and acceleration, which produces an exciting, unusual body feel. Loops, corkscrews, and tight turns force riders' bodies vertically and horizontally in calculated ways.
Ever wonder why loops are teardrop shaped, rather than circular? “The challenge is designing the transitions into and out of the loop," Rhoads says. "You need to make sure that you're not inducing jerk,” or changes in acceleration that can lead to whiplash. Anything moving in a circular motion experiences another kind of acceleration called centripetal acceleration, which increases the faster the car goes, or the smaller the circle is. A circular loop would cause a jolt from the sudden addition of the centripetal acceleration. A teardrop shape controls that acceleration, easing the rider through the loop and preventing jerk.
And then there are rolls, which can disorient riders in several ways. Inline twists are rolls that rotate trains around the track, but heartline rolls try to rotate riders around their chests. Colossus in Thorpe Park (above) is the best example of heartline rolls at work—the 90-second ride boasts 10 inversions, including four consecutive heartline rolls. “We'll see more [coasters with] multiple rolls in series one after another,” said Rhoads, “because it creates a tremendous amount of disorientation.”
Wood Versus Steel
Wooden coasters can't accommodate loops very well, so they're often less disorienting than their steel counterparts. So why is it that some riders prefer them? “People... like the anticipation, the rickety-ness of them that amps them up a little bit. They want to feel like the structure is moving underneath them,” says Rhoads. “Steel coasters are almost the exact opposite. It's like driving an antique vehicle versus driving the newest sports car.”
Wooden coasters tend not to have loops or rolls, because it would take far too much wood to support the force of a heavy roller coaster train. Hades 360 at Mt. Olympus in Wisconsin supports a roll on wooden tracks with steel scaffolding.
There are only so many ways you can fling people around in little carts by sending them up, down, and upside down. Some ride builders create compartments that roll independently from the cars, circling axes perpendicular to the track, which adds more flips without needing more loops. You can really see this on The Joker at Six Flag's Great Adventure (below).
Roller coaster experiences are more than just the sum of their accelerations, though. Other builders are adding lights, smoke, sending coasters underground, and adding “head” and “foot choppers,” close-but-not-too-close bars that provide an extra element of thrill and/or terror. “That's the trajectory we're going to follow for a while,” said Rhoads. “Bigger and faster won't be possible for much longer.”