As the roller coaster train begins its descent from the lift hill, its velocity increases. This causes the train to gain kinetic energy, which is the energy of motion. The faster the train moves, the more kinetic energy the train gains. This is shown by the equation for kinetic energy:
K = 1/2mv2
Where K is kinetic energy, m is mass in kilograms, and v is velocity in meters per second. Because the mass is constant, if the velocity is increased, the kinetic energy must also increase. This means that the kinetic energy for the roller coaster system is greatest at the bottom of the highest hill on the track: the bottom of the lift hill. When the train begins to climb the next hill on the track, the train starts to slow down, thereby decreasing its kinetic energy.