Imagine being able to travel by train without any use of an engine. The key to achieving this is gravitational force, and the idea was first proposed by Robert Hooke and Isaac Newton in the 17th century. The engineering behind this concept is pretty simple: the train would enter a tunnel that slopes down just enough for gravity to be able to move it. Halfway through the trip, the tunnel would begin sloping upwards, and the train would use the gained momentum to carry itself back up to the surface. Theoretically, the trip would take exactly 42 minutes despite any variations in the distance traveled. However, certain physical constraints prevent the excavation of any tunnel longer than 240 miles, which is around the distance from Dallas to Houston. Anything longer would pass through our planet’s thin crust, and passengers would take a one way trip straight into the Earth’s mantle. There are also factors like friction and air resistance that come into play, as well as difficulties with the actual construction of a sufficiently deep tunnel that should be considered. In the meantime, engineers are coming up with a multitude of solutions that will make this form of eco-friendly travel a reality.
Boyd, Andrew. “Engines of our Ingenuity.” Houston Public Media, NPR, 12 Dec. 2017, www.uh.edu/engines/epi2703.htm.