The converted potential energy that powers racing roller coasters
No matter how fast, how tall or how dressed up a roller coaster is, one nearly universal feature is that they lack any on-board propulsion. It’s easy to overlook when zooming over a track at over 90 miles-per-hour, but the name ‘roller coaster’ is actually really descriptive of how they move. The thrills of a good ride are just about entirely thanks to gravity converting the coaster’s potential energy into kinetic energy, all without the need for any onboard motor.
Energy released by altitude
The key to a roller coaster is just building up a battery of energy that can be doled out in its descent. Most often, that potential energy accumulates as the train or cars climb the ride’s first hill. The energy isn’t being created by the hill of course— it’s likely coming from a chemical or electrical source in the form of a generator that drives the chain that pulls the coaster. However, through this sequence of sources, the coaster arrives at the top of its first peak with a lot of extra potential energy. This then starts getting released when gravity tugs the train downhill.
As the train moves down the track, it’s basically in a guided free-fall. It increases its speed as the potential energy is converted to kinetic energy, although it’s not a perfect 1:1 ratio. Some of the energy is ‘lost’ to other components in the system, such as friction with the track and the air as the train pushes onwards. Because of these inefficiencies, the coaster won’t have enough kinetic energy left in it to make it back up the hill, perpetuating the loop. Even so, roller coasters also include braking systems that clamp down on special fins along the side of the cars to slow them to a quick stop if necessary.
How to kick off a coaster’s movement
A motor-driven chain isn’t the only way to put energy into a roller coaster, although it’s the most common. The most likely alternative is to give the coaster a big shove with some form of catapult. Some use a collection of spinning wheels to roll over part of the coaster, transferring energy into kinetic motion very quickly. To really take the motors out of the system, other catapults work more like Maglev trains. In that case, a bank of magnets on the track and the coaster can have their polarities reversed in order so that the magnetic repulsion shoves the vehicle forwards.
The last, most most unusual source of energy is likely in the Japanese Sky Cycle, which is powered by the passengers themselves. In that case, the source of power starts with riders’ food, then the mechanical transference of energy from muscles to pedals and gears as passengers have to propel themselves and the very minimal enclosure up inclines before they have a chance to enjoy the swift ride back downhill.
Source: How Roller Coasters Work by Tom Harris, How Stuff Works