adjacent to the disk by a linkage when the power is turned off. The kinetic energy of the vehicle's motion is dissipated in Joule heating by the eddy currents passing through the disk's resistance, so like conventional friction disk brakes, the disk becomes hot. Unlike in the linear brake below, the metal of the disk passes repeatedly through the magnetic field, so disk eddy current brakes get hotter than linear eddy current brakes. Japanese Shinkansen trains had employed circular eddy current brake system on trailer cars since 100 Series Shinkansen. The N700 Series Shinkansen abandoned eddy current brakes in favour of regenerative brakes, since 14 of the 16 cars in the trainset used electric motors. In regenerative brakes, the motor that drives the wheel is used as a generator to produce electric current, which can be used to charge a battery, enabling the energy to be reused. Dynamometer eddy current absorbers Most chassis dynamometers and many engine dynos use an eddy-current brake as a means of providing an electrically adjustable load on the engine. They are often referred to as an "absorber" in such applications. Inexpensive air-cooled versions are typically used on chassis dynamometers, where their inherently high-inertia steel rotors are an asset rather than a liability. Conversely, performance engine dynamometers tend to utilize low-inertia, high RPM, liquid-cooled configurations. Downsides of eddy-current absorbers in such applications, compared to expensive AC-motor based dynamometers, is their inability to provide stall-speed (zero RPM) loading or to motor the engine - for starting or motoring (downhill simulation). Since they do not actually absorb energy, provisions to transfer their radiated heat out of the test cell area must be provided. Either a high-volume air-ventilation or water-to-air heat exchanger adds additional cost and complexity. In contrast, high-end AC-motor dynamometers cleanly return the engine's power to the grid. Linear eddy current brakes Linear eddy current brakes are used on some rail vehicles, such as trains. They are used on roller coasters, to stop cars smoothly at the end of the ride. The linear eddy current brake consists of a magnetic yoke with electrical coils positioned along the rail, which are being magnetized alternating as south and north magnetic poles. This magnet does not touch the rail, but is held at a constant small distance from the rail of approximately 7 mm (the eddy current brake should not be confused with another device, the magnetic brake, which exerts