# There's a sneaky trick that is allowing this biker to seemingly defy physics by driving on water

Australian stuntman Robbie Maddison has been tearing up the waves — and the Internet — with his insanely cool dirt bike.

But how was he able to so seamlessly ride across a Tahitian wave as he would a dirt hill?

If it was a plain dirt bike, it would have been near impossible. The wheels wouldn’t be able to move fast enough to keep the bike afloat for very long.

So, Maddison added skis — like the ones you use to water ski. There’s one attached to the front wheel and one more toward the middle ending at the back wheel:

In the case of the dirt bike, the wheels were in charge of moving the bike forward as it would on land while the ski kept the bike from sinking. Arthur Schmidt, a physics professor at Northwestern University, explained in an email how the wheels were able to keep the bike moving forward:

“The motor bike has to supply its own motivation through its rear wheel,” he wrote. “A dirt bike is designed to run through mud, a fluid much like water only with dirt added. That too is not a far reach to apply to water surfing.

The most important factor, Schmidt said, is keeping the bike moving:

“The critical thing is to be able to develop enough force with the wheel treading water to oppose the frictional drag of the ski through water to maintain a speed sufficient to lift the ski and bike against gravity,” Schmidt wrote.

Remember those force diagrams you used to be asked to draw in physics class? That’s what’s happening here.

It helps that the bike was moving fast before entering the water. A couple of years ago, the Mythbusters duo tested out a similar concept, called the Aqua Bike. But mostly, this was just a regular dirt bike without the added ski. Here’s a video of how that turned out (hint: not quite as well as Maddison’s cool wave-riding stunt).

After picking up speed before entering the water, the Aqua Bike’s weight eventually becomes too heavy for the speed to counteract, causing the bike to slowly sink instead of skimming the surface. That’s what happened to Maddison as well: about 30 to 40 times in the course of this project, he told Transworld Motocross magazine.

“Honestly, the whole way I imagined I needed to ride the wave on my bike was wrong,” he told Surfer Magazine. “But after watching some footage, with my knowledge of surfing I realised I had to adjust to be up on the face of the wave — and I’m comfortable being there because I spent the majority of my life dropping in on the face of waves.”

Here’s the full video of Maddison’s ride: