Braking and Friction
The braking systems on roller coasters use kinetic friction to stop (except for magnetic brakes) by applying a force to the train via squeezing or pushing against the train or an extension of the train. Kinetic friction is the friction between two objects that are moving relative to each other. With the coefficient of friction (m) remaining constant, the magnitude of the normal force N (in this case the force will actually be the applied force from the braking mechanism) increases, causing the force of friction to increase and slow down the roller coaster car. Some brakes use magnetic fields to slow down coasters but are unable to stop the coaster completely due to the fact that magnetic fields obey the inverse square law. Thus, they must be combined with another mechanism if they are to completely stop a coaster car.
There are two categories of brakes: trim brakes and block brakes.
1. Trim brakes are used to slow down roller coaster cars but not to stop them completely. There are used in areas where the cars may be moving in a fast or dangerous manner that could cause harm to the riders or too much strain on the coaster itself.
2. Block brakes are used to the roller coaster cars from crashing into each other. They are capable of both completely stopping the cars as well as just slowing them down as trim brakes do. Block brakes also must be able to cause the cars to move again, usually via a downhill right afterwards or by pushing the car somehow.
There are three main types of brakes that have been used in roller coasters: Skid brakes, Fin brakes, and Magnetic brakes.
1. Skid brakes consist of simply a long piece of material, usually ceramic covered, that goes in between the rails of a coaster and stops the coaster by pushing against the bottom of the cars, creating a frictional force. Skid brakes are not commonly used on roller coasters being made today.
1. Fin brakes are just what they sound like, extensions of the car that hang down below the car in between controlled squeeze mechanisms. To stop the cars the squeeze mechanism, whatever it may be, closes on the fins of the cars and slows them down with friction. These are often designed to engage automatically if there is a power outage, making them fail safe. Fin brakes are the most commonly used brakes in modern roller coasters.
2. Magnetic brakes use natural forces of magnetism to stop the roller coaster cars. They consist of two rows of very strong magnets that a metallic fin will pass through. The magnets will create fields that oppose the field created by the fin and push in the opposite direction. The force created by the magnets is directly proportional to the speed of the cars and creates a smooth braking experience and reduces the risk of injuries such as whiplash. Magnetic brakes; however, cannot stop cars simply on their own since magnetic fields obey the inverse square law. They are usually just used as trim brakes or combined with another stopping mechanism to finish stopping the cars once the velocity has been reduced enough to suddenly stop without injury to those aboard. Additionally, magnetic brakes are completely silent which provide a much smoother ride combined with their ability to brake much more smoothly than frictional brakes. These brakes are being used more often in newer roller coasters.