How Do Roller Coasters Work?

The Science Behind Amusement Park Fun

Tremors roller coaster at Silverwood

It may not be as much fun as actually riding a roller coaster. But exploring how coasters work can be a great way to learn about physics. They also provide insight into engineering, design, and safety principles.

With extreme rides more popular than ever, concepts such as G-forces have seeped into our everyday lingo. Because people generally enjoy attractions like coasters (or, at least are familiar with them), they can be motivated to explore the concepts that enable rides to deliver white-knuckle thrills in a safe way.

Are you motivated? Great! Give a tug on your restraint to make sure you are snugly secured and remember to obey the no standing rule at all times as we take a ride on our moving classroom. (Also, please don't put your hands in the air. The teacher may thank you have a question.)

Superman the Ride Six Flags New England top of lift hill
Six Flags

Potential and Kinetic Energy

Since they were first introduced in the late 1800s, the general concepts that make most coasters work have stayed pretty much the same. Recently, ride designers have introduced innovations such as launch technology. For the sake of this article, however, we are going to focus mostly on the more traditional types of coasters.

On a conventional coaster, a chain pulls a train up a lift hill. In doing so, the train builds up potential energy. The chain is attached to gears at the bottom and the top of the hill. A motor turns the gear at the bottom of the hill. (Some launched coasters forego a lift chain or supplement it by catapulting trains along tracks. Most commonly, they use electromagnetic motors to launch trains.)

What connects the train to the chain and prevents it from falling back down a lift hill? Chain “dogs” on the chassis of a train latch onto the chain. They also serve as anti-rollback devices and make the classic “click-clack-click” ratcheting sound that helps build anticipation as passengers ascend the lift hill.

For traditional coasters, getting to the top of the lift hill is all the power they need. From there, gravity takes over and converts the potential energy to kinetic energy. The higher the lift hill, the more stored potential energy and the faster the train will navigate the track. There are some coasters that exceed 90 mph using nothing more than a simple chain motor (and a very tall lift hill).

Roller coaster wheels
Wikimedia Commons

Hold On!

Through the years, ride designers developed a system that uses three kinds of wheels to allow coaster trains to roll and to make sure they remain attached to the tracks. Road wheels or guide wheels roll along the tops of the tracks. Side friction wheels are mounted perpendicular to the road wheels and make sure that the train stays on course. Side friction wheels can be located on the outside or the inside of the rails. The third type of wheels are known as underfriction or upstop wheels. They are mounted under the track and prevent the train from lifting off of the rails.

There are two basic types of coasters: wooden and steel. The tracks on a wooden coaster include stacks of wood that are topped with a thin metal rail. The Matterhorn Bobsleds at Disneyland, which opened in 1959, was the first thrill machine to feature a track made of tubular steel rails. More recently, a third type of ride, known as a hybrid wooden-steel coaster, has become quite popular. It features a wooden structure with a unique kind of steel track.

Regardless of the type of coaster, they all use similar wheel assemblies. They also are subject to the same principles of physics and deliver similar forces.

© Arthur Levine.

Golly G-forces

According to Newton’s first law of motion, an object in motion tends to stay in motion. That’s why coaster trains not only race downhill, but overcome gravity and continue uphill. That’s also why the passengers in coasters want to keep moving at the same speed and in the same direction, independent of the train. When a train speeds up, slows down, and/or changes direction, its passengers experience the giddy sensations of coaster forces.

When we are firmly planted on the ground, we all experience the natural force of gravity. Known as G-forces, 1G is equal to the force that keeps us tethered to the Earth. Depending on which direction the train is moving and the amount of acceleration, some coasters can deliver crushing positive G-forces as high as 5Gs—or five times the earth’s gravitational force. Riders feel as if they are much heavier than their actual weight and may experience the restraints tightening on their bodies.

Conversely, passengers can also experience negative G-forces, also known as “airtime” aboard coasters. This is most typically felt when a train crests a hill at a high speed. The train starts falling down the other side of the hill, but thanks to Newton’s first law, the riders want to keep hurtling skyward. It is one of the features that roller coaster enthusiasts most crave. (To non-enthusiasts it can be terrifying.)

Coaster passengers also experience lateral forces, which move them left or right. Older wooden coasters typically did not have seat dividers. A few, such as the Coney Island Cyclone, maintain the traditional cars and still do not include dividers. Lateral forces can cause benchmates to slam into each other.

Steel and hybrid coasters (and, more recently, some wooden coasters) often include inversions, or track elements that send the trains and their passengers turning upside down. These include loops, corkscrews, and a wide variety of other diabolical ways to flip out riders. The inversions generate an array of forces and also alter the perceptions of passengers, which can make them very disorienting.

Many parks offer programs that allow students to learn about math and scientific principles by inviting them to conduct experiments aboard their roller coasters. The parks usually issue accelerometers to participants which they can use to calculate speed, velocity, G-forces and other data. The events, often called “Physics Day,” are typically held in the spring when schools are still in session.

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