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Re: [Phys-l] surfing



Thanks for the discussion and references. I think I've got a clearer picture now: You want to be going a bit slower than the wave (so it catches up to you) but not too much slower (so it doesn't just pass under you quickly). Then as you start riding up the sloped front of the wave, the "normal force" of the water surface pushes you forward. Presumably you then adjust your position along the slope to balance air resistance and maintain equilibrium (in the wave's frame of reference, so there is no water drag, at least until you start moving laterally along the wavefront and no longer straight toward the beach). There is an energy loss (but no change in kinetic energy after the initial acceleration up to the wave speed, my mistake indeed) equal to the air resistance times longitudinal distance moved (in the ground frame, in addition to water/air drag times lateral distance moved) which is being taken out of the wave (amplitude and/or speed, but imperceptibly small I suppose).

Next question: How does plasma wakefield acceleration (which is also often described as "surfing") work? I think there are different kinds, but I mean the kind where you fire an optical pulse into a plasma and use it as a form of particle accelerator. For the surfer, we have horizontal component of water normal force forward, and air drag backward. Taking a charge q in the plasma with the pulse arriving, what are the analogous forward and backward forces?
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Carl E Mungan, Assoc Prof of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/