Sitting on your surfboard, you glance over your shoulder and see an oncoming wave. By now, your eyes and brain have learned to time this feat just right so that you can catch and ride the wave. You begin to paddle hard, feeling the acceleration as the water boosts you to match its speed. As you stand and balance on the board, you show off with some turns. Then, you decide to end your ride by stepping back on the board and drop the tail into the water, putting on the brakes. Ever wonder about the physics behind the sport of surfing and how everything comes into play just right so you can catch that perfect wave?
Gravity and Buoyancy
While you are lying on your board waiting to catch a wave, both gravity and buoyancy are at work. Gravity pulls on every inch of you and your board. Your centre of mass is typically located behind your navel in the middle of the body when you stand upright. It is this centre point that allows you to rest in balance. Buoyancy is an upward force that is created by resting waters pushing on the board. Also known as hydrostatic force, it is exerted by the water onto every inch of the board, particularly at the board’s centre of mass.
If you are just learning how to surf, the most important thing you need to master is balance. If both the upward force of buoyancy and the downward force of gravity are in line, they equal zero and you are stable. If you slide backward on the board, gravity moves behind the buoyant force, thus creating a torque that twists the board.
As the wave reaches you, it will be traveling at roughly seven miles per hour or six knots. As you start to paddle, you accelerate to a speed that will let you catch the wave. As you push the water backward with your hands, the water pushes you in the opposite direction by Newton’s Third Law of Motion. As the wave reaches you, the water tips upward and you are on a slippery slope; buoyancy pushes you up while gravity pulls you down and hydrodynamic forces exerted by a moving fluid are pushing you forward.
The Wave Breaks
As the wave moves into shallow water and breaks, you lean to the side so that you can stay on the wave ahead of the break on its steepest part. By riding these waves, you are playing with energy; as you are pulled by gravity and drop down the face of the wave, you are gaining the energy of motion, or kinetic energy. Simultaneously, you lose the energy of being higher in elevation, or the gravitational potential energy.
You are Finished
As you finish riding the wave, you step back on the board and effectively apply the brakes by digging in the rear of the board. You land on the back of the board, ready to paddle out and catch another wave.
Matt is a keen surfer and is always seeking out new waves and challenges. He recommends getting a quality surfboard from Fellow, where you can also grab some unique apparel, and be ready to hit the waves and conditions in comfort and style.
Photo Credits: Wikipedia