"Piled Higher and Deeper", the web comic strip also known as PhD Comics, has dedicated an episode to the science behind waves and surfing, in Waikiki Beach, Hawaii.

"Physics, Cartoonists, and Surfing, Oh My" is a simple, rich and entertaining video lesson about the physics of surfing. Where do waves come from? What are the physics involved in the act of surfing?

They are PhD Comics and they always want to know why, so Jorge Cham invited Assaf Azouri, a PhD student at the University of Hawaii at Manoa, to explain how and why we ride waves in the surface of the oceans.

Assaf studies Physical Oceanography, that is movements of currents. He is especially interested in seiche, a standing wave in an enclosed or partially enclosed body of water that can cause damage in harbours, for example.

In a eight minutes we learn that longer waves travel faster than shorter waves and that the Navier-Stokes equations explain the motion of fluid substances and, therefore, waves.

The gravitational force, buoyancy force and drag force (friction) are the main variables at stake, when you paddle for a surfing wave.

To catch a wave, you have to move at the speed of it, so you have to paddle in order to reach the same speed of the wave. It's a balance between forces that makes surfing.

I will never forget the surfboard that got me into surfing. It was not a board like the ones I see today in fancy surf shops. It was the most important object I owned in my life.

Alexandre Caizergues has broken his own world speed kiteboarding record.

Zara Davis has broken the women's speed windsurfing world record, at the 2017 Luderitz Speed Challenge, in Namibia.

What happens when a cute duck family tries to jump out of a swimming pool? You give bodyboards a new use as a rescue device.

Whether you're a flatland skim rider or a wave skimboarder, you need to learn to throw the board before jumping on it.

Nico von Lerchenfeld has had the time of his life at Surf Snowdonia, in Wales. But he was not there to surf.