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Meet mechanical engineer and roller coaster designer Chris Gray, in this video adapted from DESIGN SQUAD. Mechanical engineers use their knowledge of science to design and build all kinds of machines, including roller coasters. Chris explains how gravity and the changes in energy—between its potential and kinetic forms—create the excitement of a roller coaster ride.
This video is available in both English and Spanish audio, along with corresponding closed captions.
This media asset is adapted from DESIGN SQUAD: "Roller Coasters."
Energy is an important engineering concept in roller coaster design. Roller coasters do not have their own engines. The cars are pulled by a chain to the top of the starting hill and then released. After that, gravity and transfer of energy keep them moving along the track.
On Earth, gravity is the force that pulls objects toward the ground. Potential energy, often referred to as stored energy, is the energy of position. To establish enough potential energy in the cars at the beginning of the ride to let them coast to the end of the ride, designers must make sure the cars start to descend from high off the ground. As gravity pulls the cars downward, potential energy is transferred into kinetic energy—the energy of motion. Then as the cars ascend the next hill, kinetic energy is transferred back to potential energy. The sum of an object’s potential and kinetic energy at any moment is called its mechanical energy.
When you lift an object off the ground, you use your own energy to work against the force of gravity. You also transfer this energy to the object. In the same way, the energy used to pull roller coaster cars up the first hill is transferred from the chain to the cars when they reach the top. Potential energy is the weight of an object multiplied by its height. The higher off the ground an object is, the more potential energy it will have. The potential energy will convert to kinetic energy if the object falls. This explains why roller coaster rides have their tallest hill near the beginning of the track.
But roller coaster designers must also allow for another factor when they calculate how much potential energy will be enough for the ride. The transfer between potential and kinetic energy is not perfect. A force called friction actually takes away some of the cars' total mechanical energy during the ride. Friction results from objects touching as they move past each other.
In a roller coaster ride, friction occurs between the cars’ wheels and the surface of the track. The mechanical energy taken away by friction does not disappear. Instead, it gets transferred from the wheels to the track as thermal energy, or heat. Thus, engineers must work out how much energy will be lost to friction before deciding on the height of the starting hill. They must also make sure every hill along the track is small enough so that the kinetic energy of the cars at the beginning of that hill is enough to move them over the top. As cars move up and over each hill, they have a little less energy for the next one because of friction.
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