Part of Every Moving Train Travels Backwards — Here's Why

Stick a piece of tape on a bicycle tyre and watch it as the bike rolls past. Near the ground it looks sharp. At the top it becomes a blur. Same tape, same wheel, same instant. The top of a rolling wheel moves at twice the speed of the vehicle. The bottom, at the moment it touches the road, is completely at rest. This video builds the whole idea from scratch — why a rolling wheel is really two motions added together, why rolling without slipping forces the spin speed to equal the travel speed, and what that means for the tyre in contact with the road. Then it goes further. Why this is the reason tyres grip at all, what actually fails during a skid, and why anti-lock braking exists. Then the curve a rim point really draws through the air, which is not a circle. And finally the train wheel, where the flange hangs below the rail and parts of it genuinely travel backwards relative to the ground while the train races forward. The question comes from Yakov Perelman's Physics for Entertainment. The explanations are my own. More physics from everyday machines coming. Subscribe. #physics #engineering #automotive #rollingmotion