Physics debate settled: faster than the wind is possible

A wind-powered car has reached a top speed of 38.61 miles per hour (62 kilometers per hour). By itself that might not sound impressive, but it appears to answer a long-running physics question: can a wind powered vehicle travel downwind at a speed faster than said wind.

The main argument against such a possibility is that it would create perpetual motion, meaning that once the vehicle started it would never stop. It’s generally held that this would violate the laws of thermodynamics. However, supporters of the “downwind faster than the wind” idea have argued it is not perpetual motion.

In the past, there have been no full-scale demonstrations that the theory holds up in reality. Instead there have been a variety of demonstrations using small models on a treadmill. The treadmill isn’t cheating, but rather a way to recreate a “perfectly straight road that’s perfectly aligned with a perfectly steady wind”, which is easy to assume in physics theory, but trickier to achieve in the real world.

That is until a project run by Rick Cavallero, the chief scientist at Sportvision Inc. His team received funding from Google and wind turbine firm Joby Energy, and worked with San Jose State University’s aero department.

They’ve now built a vehicle known as Blackbird and repeatedly achieved speeds of 2.85 times faster than the wind which was powering the car.

The key to this achievement is that the wind doesn’t directly turn the propeller. Instead the wind pushes the vehicle and the wheels turn the propeller (in the opposite direction to normal wind-powered vehicles). This pushes the wind backwards and thus creates more forward momentum for the vehicle.

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