The Science Behind Roller Coasters

They're one of the most popular theme park attractions. Their gravity-defying loops and twists keep visitors coming back again and again.

Roller coasters have been around since the 1800s. The technology has come a long way since then — and some of the newest roller coasters can reach speeds of up to 140 miles per hour. But how do roller coasters work? And how do engineers build a ride that they know will make it from start to finish? To explain, we'll need to start with a simple lesson in engineering and physics.

The Physics of Roller Coasters

Roller coasters use two different kinds of energy to move. Roller coasters are powered by potential energy — the energy you get from being high up and pulled down by gravity. In traditional roller coaster design, the carts are pulled to the top of a hill and then released. When the carts are released, that potential energy is converted to kinetic energy — forward motion and high speed.

Some roller coasters rely on complex hydraulic systems that launch roller coasters out of the start.

The body can't feel velocity, which is why it's possible to travel over long distances on ultra-fast bullet trains. The body does feel changes in velocity, however. These changes are called acceleration. On the track, all the hills, turns and loops create rapid changes in direction and acceleration to cause a range of physical experiences — like the feeling of being pulled one way, then another, then totally weightless as the coaster moves.

Roller coaster acceleration is measured in g-forces, or how strong the acceleration is compared to the force of gravity. Some of the wildest coasters have riders feeling forces of more than six times the strength of gravity.

How an Engineer Sees a Roller Coaster

Roller coasters have more speed than they need to naturally glide to a stop at the end of the ride. So, most roller coasters include brakes that bring the coaster to a halt.

Part of this is to account for kinetic energy lost to friction over the course of one ride. Roller coasters — especially more modern designs — are built to glide across the rails, minimizing contact and speed lost to friction. But all roller coasters lose some amount of speed to friction, and roller coaster engineers must account for it.

There are different brake types on roller coasters. Block brakes bring the ride to a complete stop. Trim brakes are used to slow down the ride at certain points and ensure that the acceleration and g-forces generated by the ride remain at the right levels. The brakes use special hydraulics to slow down the heavy and fast-moving coaster.

Like buildings, bridges and any structure that needs to withstand high forces for a long period of time, roller coasters are naturally designed with some overage in mind. The first hill will be higher than theoretically necessary to account for all that lost energy, for example. And the loops and metal corkscrews will be built to handle more force than the coaster can produce. These overages help to ensure that the side is as safe for riders as can be, while still delivering the experience people expect from a roller coaster.

Some new roller coasters use computers to track where carts are and hold back new carts from launch to ensure there's a healthy amount of space between the two.

There are other, newer types of roller coasters than the standard steel or wooden coasters. For example, "4D" roller coasters use a combination of on-rails sections and complex hydraulic systems to create a new kind of experience. But the physics for roller coasters is mostly the same whether the coaster is an inverted or suspended coaster or uses computers to ensure rider safety.

Thrill and Energy

Roller coasters rely on gravity and changes in speed to create feelings of being pulled one way or another as well as weightlessness. And like other major structures, they're built with safety in mind. With the addition of advanced hydraulics and computer technology to bring roller coasters to a complete stop, roller coasters deliver high-energy thrills without any real peril.