Are you ready for some excitement? Today in Wonderopolis we're headed to the amusement park to take a spin on that hair-raising, scream-inducing ride we know as the roller coaster!

Have you ever looked closely at a roller coaster, though? Did you realize it doesn't have an engine? Have you ever stopped to WONDER how a roller coaster operates at such high speeds without one? Let's take a look at the scientific principles and forces behind the thrills of the roller coaster.

Since roller coasters don't have engines, they must be pulled by a motorized chain to the top of the first big hill. As the roller coaster rises higher and higher into the air, its potential energy keeps growing until it reaches its maximum potential energy at the crest of the hill.

Potential energy is sometimes known as positional energy. Potential energy represents the amount of work the roller coaster will be able to do with the energy it builds up from falling down the other side of the hill.

And why does it fall down that hill? It's the same reason you fall down when you trip. Or why a ball hits the ground when you drop it. What are we talking about? Gravity, of course!

When a roller coaster crests the first big hill, gravity takes over, causing the roller coaster to fall down at a constant rate of 9.8 meters per second squared. All that stored potential energy changes to kinetic energy, which can also be thought of as moving energy.

As the roller coaster falls, it accelerates and builds up enough kinetic energy to propel it through the remainder of the ride. No engine is required because of inertia. Inertia is one of the laws of physics described long ago by Sir Isaac Newton. The law of inertia holds that an object in motion will stay in motion until acted upon by an equal but opposite force.

In the case of a roller coaster, this means that the kinetic energy built up from the fall down the first hill could keep it going forever. We all know, though, that roller coaster rides don't last forever. That's because the roller coaster loses energy to other forces as it does loop-the-loops, curves, and other hills along the way.

These other forces eventually bring the roller coaster to a stop, albeit with some help from air brakes at the very end of the ride. So what are these other forces? Two of the most significant are friction and air resistance. As you ride a roller coaster, its wheels rub along the rails, creating heat as a result of friction. This friction slows the roller coaster gradually, as does the air that you fly through as you ride the ride.

Roller coaster rides are so exciting (or terrifying!) for some people because of the other forces at work on your body during the ride. The forces of gravity and acceleration that move the roller coaster along the track also affect your body in the same ways.

For example, when you go around a sharp curve or a loop-the-loop, special forces of acceleration push you in different directions. Not only do these forces keep you in your seat, but they also are responsible for the exhilarating feelings you get that some people call a “rush."

Some people also love the weightless feeling you get briefly at the top of a loop-the-loop. That feeling you get is caused by two forces countering one another: gravity is pulling you toward the ground at the same time as inertia is pulling you toward the top of the loop.

If you want to ride the world's fastest roller coaster, you'll need to catch a flight to Ferrari World in Abu Dhabi, which is part of the United Arab Emirates. There you can ride the Formula Rossa, which reaches an amazing top speed of 149.1 miles per hour. The ride is so intense that passengers must wear goggles to protect their eyes!

#### Wonder What's Next?

Tomorrow’s Wonder of the Day is swinging for the bleachers!