Sea surfer position displacement Waves are means by which the energy propagates through a medium (e.g., sea water). This is not associated with a net movement of water in the direction of wave propagation. If this is the case, then how does a surfer move with sea waves toward the seashore?
 A: First things first: waves that have already reached close vicinity to the beach DO displace water towards the shoreline - just notice how the water moves back and forth at the point it's ankle-deep. This is related to the phenomenon by which they lose their wave form and get a crest.
There are many forces acting on a surfer, but two of them are the important ones here:


*

*Buoyancy

*Gravity


Buoyancy acts to "push" the board on a normal (while on (and relative to) the surface), while gravity is always acting to pull the surfer downwards. As a wave is moving through the water, you'd get an arrangement kinda like this (forgive my use of ASCII art):
.\  <- wave
..\
....\   SURFER
.....\
.......\___ <- sea surface right ahead of wave
...................................................................................
...................................................................................
In the drawing above, the dots to the left of the dashes and below the text are water.
Since buoyancy is normal to the wave front and gravity pulls you down, the resultant force will be such that you will be sliding down the wave. It will push you along until it breaks, or until it gets past you.
If you do try to surf on deep sea crestless waves, then waves will still push you around - but you won't be sliding any particular wave indefinetely. The net displacements you get by being on the "front" and "back" of each wave will mostly cancel out, and you will be stuck in the same place. Better bring a sailboard.
A: I think there are 3 factors :  1- gravity, 2- the upward movement of water by wave propagation (and this is the on that works in opposition to gravity) & 3- the displacement of water towards shore. The latter is caused by the fact that the front-face of the water moves slower than the hind-face which causes the shape of the wave to curl.Now, how does the third factor causes water to displace ?. I think it's fairly simple, since the crest of the wave is curled the water of this part will simply drop down in front of the wave base , the process is repeated continuously and therefore each chunk of water will get displaced toward the shore.Notice that I assumed that the wave has a velocity gradient across it, and what made me do so is that I've remembered something about how the vine plants do curl and that is by using a growth-speed gradient across its tendrils to cause them to curl. Sorry for using biology analogy !.
