Question

Describe the physics of surfing on a long board, consider the temperature to be approximately 90 degrees Fahrenheit. Use the concepts from mechanical waves & sound and fluid mechanics to contribute to the answer.

Answer 1

A longer surfboard causes more friction with the water; therefore, it will be slower than a smaller and lighter board. Longer boards are good for beginners who need help balancing. Smaller boards are good for more experienced surfers who want to have more control and maneuverability

When the surfer is at wave speed, the surfer must quickly pop up, stay low, and stay toward the front of the wave to become stable and prevent falling as the wave steepens. The acceleration is less toward the front than toward the back. The physics behind the surfing of the wave involves the horizontal acceleration force (F·sinθ) and the vertical force (F·cosθ=mg). Therefore, the surfer should lean forward to gain speed, and lean on the back foot to brake. Also, to increase the length of the ride of the wave, the surfer should travel parallel to the wave crest.

Following are the factors affecting surfing.

1) Buoyancy: The surfboard's buoyancy, or ability to float, comes from its density. The board is less dense than the water underneath it. The board's coating is also waterproof, keeping water from seeping in, soaking the foam inside and pulling the board under.

2) Surface tension: The molecules that make up water are attracted to one another, so they create a surprisingly strong film at the water's surface. This film is one reason why a wave holds it shape, and it helps keep the surfboard afloat.

3) Gravity: While buoyancy keeps the surfboard afloat, gravity pulls it and its rider toward the water. Gravity's pull helps the rider hold his position on the moving, nearly-vertical face of a wave.

4) Mass and shape: The surfboard and its rider both have a center of gravity, which is related to their shape and mass. When riding the waves, the rider can move his center of gravity to shift the board's angle in the water. For example, moving toward the tail of the board will cause the nose to lift up from the water in response.

5) Hydrodynamic forces: Hydrodynamic forces are essentially the same as aerodynamic forces. These forces, like lift and drag, can dramatically affect how waves form and how the waves interact with the surfer's board.