Can anyone verify that I'm thinking about this situation correctly: among cyclists, there exists a thing called a roller trainer, which allows cyclists (or anyone who wants a workout) to train indoors (eg when it's too cold out). It looks like this: http://www.fact-canada.com/Tacx/Tacx%20Antares.jpg [Broken] These typically don't provide enough resistance to provide proper training, so resistance units are added. Usually they take the form of units that interface mechanically with the belt or roller somehow, but the cleverest ones are just magnets that ride behind the metal rollers (usually aluminum), which look like this: http://www.sportcrafters.com/sportcraftersimages/resistanceunit.jpg [Broken] This is a case of a loop moving through a B field. And the relationship between speed (i.e. speed of the rollers at the point closest to the B field) and force (the resistance the unit provides) is linear, correct? Any other comment or anything I'm missing? I have a set of these at home, and I'd be curious to know how much current is running through these, but I think I'd have too many not-trvially-measured unknowns.