Pro road racers who use Berner's uniquely oversized rear derailleur cages have sworn time and again that they reduce drivetrain friction thanks to their humongous 15-tooth pulleys. Now, Jason Smith of ...

The kids learn about pulleys. / Sally learns about a force called friction. The kids want to get a trunk up into the treehouse and go to the Machine-a-Ma-Zoo, where they’re introduced to simple ...

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