Kinetic and Potential
Kinetic Energy is energy in motion, like falling down a hill, or going down a hill on a roller coaster.
Potential Energy is the energy in a position ready to be in motion, like a skier at the top of a slope.
In the first 40 seconds or so is the beginning of the build of potential energy. Just at the top when it starts to go down it releases that energy which becomes kinetic energy to make train go faster.
Another vocabulary word that relates to the video would be Mechanical Energy. This kind of energy gathers energy from its motion or position.