Rollercoaster trains have no engine or no power source of their own. Instead, they rely on a supply of potential energy that is converted to kinetic energy. Traditionally, a rollercoaster relies on gravitational potential energy – the energy it possesses due to its height.

A roller coaster is primarily a machine that exploits the conversion of potential energy into kinetic energy. Most traditional coasters do not have an engine; instead, they are propelled to the top of a "lift hill" by a motorized chain or cable. Once the train reaches the summit, gravity takes over, pulling it down the slope and converting its stored potential energy into the kinetic energy (speed) needed to complete the circuit. Modern "launch" coasters use more advanced systems like Linear Induction Motors (LIM) or Linear Synchronous Motors (LSM), which use powerful electromagnets to propel the train from a standstill to high speeds in seconds. Other systems include hydraulic launches, which use pressurized fluid and a winch, or pneumatic launches using compressed air. Once in motion, the train's inertia keeps it moving through loops and turns, while friction and air resistance gradually slow it down until the final brake run.