Have you ever tried surfing and gave up? Don’t feel guilty. Surfing on a board is like a crash course in classical mechanics: only at the end you learn to find the perfect balance between rapidly changing physical forces acting in different directions.

Surfing and Archimedes. Even with the sea calm and confined to lying face down on a table, gravity and Archimedes’ strength are in competition. The first pushes the surfer and their board down, and the second responds with an upward directed force equal to the weight of the moving water.

Since the slab is made of a material less dense than the water underneath, buoyancy prevails over it. Then there is the wave, of course, the intrinsic physical phenomenon. Transfer of energy from a water molecule to a water molecule that can cross the sea for miles; Near the shore, the bottom of the wave creates friction with the sea floor, while the top rises and produces a crest.

Surface tension also plays a role, which is the force that causes water molecules to attract each other, creating a kind of film: it helps maintain the wave’s shape and helps it float away from the board. As every surfer knows, when a wave approaches it is not enough just to stand aside and wait for it. You have to expect and swim to gain speed before you get stuck.

Newton is also involved. Ideally, the surfer should be at the same speed as the wave, that is, with enough kinetic energy for the wave to move a little, to keep the board moving and to overcome the friction of the water, which in turn can stop it. A few meters away. A perfect explanation of Newton’s first law, which states that a body in a uniform straight motion tends to keep moving.

———————————

Taken from Nicola Nosingo’s article published in Focus 346 – August 2021.