Electromagnetic propulsion uses strong electrical impulses to attract or repulse magnetic fins attached to the vehicles. The stator and rotor are laid out in a line (as opposed to a torque or rotation) which produces a linear force and contains no moving parts. This propulsion system is fairly popular because it offers a very precise control of speed. The acceleration from the launch is greatest at the beginning and dies off rapidly towards the end of the launch. There are two types of electromagnetic propulsion used on roller coasters: linear induction motors (LIM) and linear synchronous motors (LSM).