Re: [Phys-l] surfing

[Carl Mungan <mungan@usna.edu>]

John Sohl wrote:

> The key issue is that you need to go down hill as fast as the hill catches up
> to you. In other words, you need to be on a steep part of the wave so that you
> have a gravitational force that speeds up the board as it "falls down the wave
> front."

Thanks, that's an interesting starting point to think about things. 
But I don't really get it - surfers don't seem to change altitude 
much as they surf. Thus, the kinetic energy they acquire doesn't seem 
to come from (direct) change in gravitational PE. I assume they "suck 
it" out of the water wave somehow (presumably at the expense of the 
wave losing some amplitude or speed, or more likely both as they're 
probably connected to each other).

Your description however does helpfully draw attention to the fact 
that a surfer needs to gain a certain amount of speed before the wave 
arrives. How closely they need to match the wave's speed before 
"catching it" is not obvious to me. Based on "boogie boarding" (or 
even just "body surfing") it seems like I can be a bit under speed 
and suddenly get "jerked" up to the correct speed -- the more crucial 
bit being how far from shore I'm located when the wave breaks, rather 
than my exact speed. Why is that?

Right about now, I'm wondering whether anyone knows of a good 
"physics of surfing" review article. -Carl
--
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/