You can’t leave Hawaii without taking a surfing lesson.
So, during a recent reporting trip to the island state, I hit the beach for a 90-minute tutorial.
I already knew how to skimboard — the miniature, not-as-cool version of surfing. Riding a big, buoyant board down a rolling hydrodynamic construct most people call a wave, however, is different.
I learned surfing boils down to some pretty simple physics, and thinking through all of the different forces helped me get the hang of it.
Step 1: Catch a wave
I booked a lesson in Kona on the big island of Hawaii. After subduing my irrational fear of sharks, I grabbed a surfboard, an instructor, and paddled out into the Pacific Ocean.
Thankfully, there are no monster-sized waves in Kona during the summer. They’re mostly beginner-sized, which was perfect for me.
But small waves can move pretty fast. My instructor said they move at around 8-10 mph — about the speed of a leisurely bike ride. To catch a wave, you have to get in front so that it doesn’t roll under you.
The problem is that it’s nearly impossible to paddle as fast as a wave rolls. So surfers use a different method: They tap into the wave’s gravitational potential energy.
You only have to paddle fast enough so that, as the wave starts passing by, you and your board lift up and start slipping down the face of the wave.
As you fall down the face, your gravitational potential energy converts into kinetic energy. If you keep going straight, you can build up enough energy to just outrun the wave as it drags you back up. That equilibrium is called, well, surfing.
If you want to catch a monster wave, however, you’ll need some kind of watercraft to tow and pull you. Humongous waves move at speeds of around 35 mph, and there’s simply no way a surfer can paddle fast enough to rely on gravitational potential energy alone.
Step 2: Stand up on the board
This is supposed to be the hard part, but standing up part can be surprisingly simple.
As you slide down the face of the wave, you can feel the wave lift up your board’s tail end. It feels like the wave is going to flip you over, but that’s when you paddle a couple more times then quickly (and carefully) lift yourself up on your feet to balance out the board.
Arching your back is crucial. You want most of your weight to stay low and near the back of the board; otherwise, you’re in for head-over-heels wipeout.
A successful stand-up looks something like this:
Step 3: Enjoy the ride (while not falling off)
Just riding down a wave and using gravitational potential energy to outrun it is only half the fun.
Once you get the hang of standing up, the idea is to turn the board and surf across the face of a wave. To do this you need to create a little torque, aka twisting force.
Every surf board has a center of mass: where the downward force of gravity and the upward force of buoyancy meet.
When you step back on the board, you move the upward and downward forces out of alignment. This creates the opportunity to generate torque, at least until the wave peters out and gravity and buoyancy line up again (or you wipe out).
Stepping back and shifting the weight on your back foot to either your heel or toes will let you turn and ride across the wave.
One more tip: You often see surfers holding their arms perpendicular to their bodies.
They do this to help control torque, and it just so happens that moving your forward arm in the direction you want to go helps steer you that way.
My 90-minute lesson didn’t last nearly long enough for me to master turning, and I wiped out more times trying than I’d like to admit.
Beyond the concepts of gravity, buoyancy, and torque, there’s a whole host of hydrodynamic forces at play in surfing, too. They shape the ocean waves, and push and pull on the surfboard. They’re also why a board’s length, fins, contours, and other design aspects are so important, and surfing in general takes a lot of practice to do well.
But thinking through the basic physics at least helped me learn how to catch a wave, find my balance, stop thinking, and just enjoy a few rides to shore.
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