What really causes the train to accelerate or brake are the adhesion forces that appear in the wheel-rail contact. For these adhesion forces to appear, tractive or braking effort needs to be applied to the wheels. This torque must be generated in a motor or braking system that transforms a certain amount of energy into the required mechanical energy. These three stages form a general summary of the fundamentals of railway traction. All that needs to be done is to develop a simple model that looks at the phenomena produced from an energy point of view, from the moment the energy is captured until it reaches the wheel-rail contact. As a result of all this, the train accelerates or brakes.