Roller coasters have long been identified as a staple of the American amusement industry, thanks to the huge success of Six Flags Great America. But roller coasters actually originated in Russia in the 17th century. These original roller coasters were originally known as ice slides and were centered in St. Petersburg. They were constructed of wood with a layer of ice several inches thick covering the surface. The people who cleared these slides climbed the stairs at the back of the slide, then accelerated down the 50-degree drop. These ice slides were built between 70 and 80 feet tall that spanned hundreds of feet and accommodated many large sleds at a time. The French are later credited with adding wheels to ice sleds and showcasing cars that got stuck on the rink. With this new design the French roller coaster was even capable of long twists and turns and even loops (the first loop roller coasters were made in France). It wasn't until the French gradually lost interest in roller coasters that a man named Marcus Thompson created the first roller coaster in America. In his original designs Thompson used many of the design layouts used by the Russians with their ice slides. Some of the first accidents specifically occurred in the late 1800s and early 1900s, when roller coasters were still relatively new to America. However, countless accidents occurred at Coney Island in 1900. Some incidents include in 1937, when two girls were on a ride called the Octopus, when the rides they were in simply went out of order and they fell. Another accident occurred in 1925 when a woman riding "The Thunderbolt" was thrown forward and struck her head on the metal bar in front of her. Yet another accident at Coney Island occurred where a train... in the middle of a sheet of paper... while trying to represent the forces acting on a passenger on a racetrack. In terms of force, friction, potential energy, gravity, velocity, acceleration, and kinetic energy, roller coasters accelerate and change direction frequently and at high speeds. When you go up a hill, the roller coaster stores potential energy that will be converted into kinetic energy on the way down. Friction on a roller coaster comes in the form of wheels to keep the car on the track, brakes to stop the roller coaster at the end of the track, air resistance, and the tracks themselves. In terms of forces, roller coasters only use gravitational force and the normal force of the seat pushing up during the ride and the weight of the rider. Roller coasters must overcome gravitational force to get over hills and need normal seat force pushing the rider up to get over the loops.