I know/think that a part of the coaster passes through a magnetic field, and because of the change in flux, an eddy current is created, which causes a Lorentz force that opposes his ‘creator‘. But where is this eddy current?And where can I find how strong the magnetic fields are in different coasters?(excuse any wrong terminology, I‘m dutch :P)
How Do Roller Coasters Work
The eddy current is in the non-magnetic metal. In this case, the rail.
There is a conductive, material installed for that purpose. It can be either non-magnetic or magnetic. Since it is in the flux path magnetic material can be useful, but magnetic materials are usually not the best conductors. In some eddy-current brake designs, copper plated steel has been used. There a couple of pictures in the pedia article on eddy-current brakes. If you can find good pictures and see the size of the coils, you may be able to estimate the magnetic field.
