It all started with a joy ride in a wind-powered vehicle. Science YouTuber Derek Muller claimed he could use the  car to cruise faster than the wind while traveling directly downwind, using only the power of the wind. Alexander Kusenko, a professor of physics at the University of California, said such a feat would break the laws of physics. The pair made a $10,000 bet to see if Muller could prove it.

The physicist lost and the science YouTuber won.

The wind-powered car looks like a windmill attached to a rickety F1 racer, but it’s more complicated. The car's wheels power the turbine and the propeller spins backwards, generating thrust. Racing downwind, the propeller spins faster and so do the wheels, pushing the car faster than the initial wind speed. According to Kusenko, the greater speeds are caused by random gusts and inertia. He was willing to put $10,000 on the line if Muller could prove otherwise.

Muller did. “When the speed of the car is exactly equal to the speed of the wind, it seems like the propeller can provide infinite force,” Muller said in his video, citing one of Kusenko’s biggest problems with the experiment. “This is exactly what you’d expect with any lever or pulley. If one arm of the lever is zero, then you can lift an infinite weight with any amount of force on the other side.”

As a proof of concept, Muller teamed with YouTuber Xyla Foxlin to build a model downwind cart which they ran on a treadmill. After working out some design flaws, Foxlin’s cart would always gain speed and move faster than the treadmill.

“Professor Kusenko has now conceded the bet,” Muller said on YouTue. “And he transferred $10,000 to me. I want to thank him for being a man of honor and changing his mind in light of the evidence presented.”

Muller said he plans to give the money away as part of a science communication competition.