Physics of the Flip Flap Rollercoaster
On January 20, 1885, the inventor, LaMarcus Thompson of Coney Island, New York, received the first patent for a roller coaster. Called the Gravity Pleasure Switchback Railway, this roller coaster was a cart that traveled down a 600-foot mini-railway at a leisurely six miles per hour. It was quaint.
Ten years later, Coney Island debuted their roller coaster called the Flip Flap Railway, which was the first roller coaster with a loop. If you have listened to my podcast, you learn that many people suffered whiplash, neck injuries, and even ejection.
What engineers didn’t understand then was the effect of gravity forces on the human body, mostly because they were testing out the roller coaster with a heavy bag of sand. Technically our bodies can only handle a force of 5 Gs. However, the Flip Flap made its thrill seekers endure 12 Gs on the body! Anything over five can be detrimental to the human body. Twelve Gs can cause gravity-induced loss of consciousness, which pilots refer to as GLOC. Brian D. Avery provides a fantastic Ted-Ed video that explains how a large G force can affect your body … for the worse! You can find it here:
What our early roller coaster engineers did not understand is that our bodies are accelerometers. We feel the acceleration. This is the key factor to what we feel when we are in a roller coaster because the roller coaster is propelled entirely by the power of gravity. We feel the roller coaster obtain potential energy (while we undergo heart-racing anticipation) as we slowly climb up the roller coaster from the lift hill.
Or we feel a sudden burst of energy as the roller coaster rapidly hurls us forward from a hydraulic launch system. Here is an excellent video from SciShow that helps explain how the hydraulic launch system works on roller coasters.
At the top of the hill, the rollercoaster has potential energy. No matter how you got to the top of the first hill or mountain, the best part about the roller coaster is the feel of weightlessness as the potential energy turns into glorious kinetic energy, and you go into a state that feels like free-fall.
So our bodies experience the pull of gravity as we climb the hill while the coaster gains potential energy, or our bodies are floating above the seat on a small scale during the descent down the hill as we experience kinetic energy.
We feel gravity on our bodies as we stand or sit. That force that we are used to daily is just 1 G. It’s a contact force that we get from the earth, also known as the Normal force. It is called Normal because that’s a synonym for perpendicular. The Normal force is perpendicular to the surface that you stand on. The image of the box on the table helps to explain this. Even though the box is at rest on the table, two forces are acting on the box, the Normal force N, and the force of weight W. The force W is the weight of the box, and the force N is the upward force that the table exerts on the box.
But when we are falling from a high point on a roller coaster, there’s no Normal force pushing up on us and we are free falling at 9.8 m/s2, which is the force of gravity pulling us down. And, again, since our bodies are accelerometers, we feel this…and it’s awesome. We are accelerating towards the earth at 9.8 m/s2. That is gravity, showing us a good time!
Now, for the Flip Flap. What went wrong? Well, for all looping roller coasters, as a roller coaster is going into a loop, the speed at which we move provides us the inertial velocity to get to the top of the loop and then back down again. If you have even been in a looping roller coaster, you will feel heaviest at the bottom and the lightest at the top. Two vector forces are acting on the body, the Normal force and gravity’s force. What we actually feel on our body is the Normal force. As a result, as the velocity moves us forward, the net force on our bodies keeps constantly changing. The net force will always have an inward direction on the loop.
Khan Academy provides an excellent video on calculating the Normal force, which you can find here:
As the coaster moves to the top of the loop, passengers should feel a sense of weightlessness. Again, that’s the Normal force that we feel, and the Normal force is minimal. But, for the Flip Flap, once that coaster started to go back down, gravity began to pull on it. The Flip Flap was a perfect circle, so the loop’s curvature was constant. Looking at the images, we see that because the net force points inward. Once the coaster reached the bottom of the track, the Normal force is much bigger than the force of gravity. That Normal force was much stronger than the force of gravity, and it was exerted on the passenger sitting on the wooden cart. At that instant, the Flap Flap passengers endured 12 Gs on the base of their spines. In a wooden cart!
Also, the passenger cart was going in too fast in order to get it through the whole loop. As a result, the magnitude of the G force increased instantaneously at the entrance of the loop and at the exit of the loop! This fantastic video created by The Art of Engineering explains this perfectly at 7:08. However, I recommend watching the whole video because it perfectly illustrates the math and physics behind the circular loop. It also describes how the clothoid teardrop shape that we now use creates a gradual change in curvature and reduces the maximum force at the bottom of the loop.
Today the roller coaster is controlled and not as crazy as the original roller coasters of the 19th century. We now have standards in place that are set forth by the American Society for Testing and Materials https://www.astm.org/ that present G force exposure limits. These G force limits incorporate facets of physics and design. Also, thanks to 3D modeling and computer analysis, we can now design some fantastic roller coasters that can be tested in a virtual environment to ensure your safety. So, if you are on a roller coaster that makes you feel like you want to die, don’t worry, we have some talented and brilliant people on the job making sure that you’re just fine.