waves

[nibot]

One of the things I was taught in elementary school that has long bothered me is that "in [ocean] waves, the water isn't moving, it's just the effect that's moving." Watching the surfers outside my window (ha!), I can't help but remember this. Of course the spirit of the statement is correct, but the problem is that water is not a particularly compressable fluid, so conservation of mass says that water has to be moving. eh?

Comments

[kaolinfire.livejournal.com]

well, the water's moving up and down, surely enough. just not traveling into shore so much... right?

[nibot.livejournal.com]

the point is that water can't stretch (it's incompressible), and there isn't going to be a vaccuum... so how can the whole column of water move up or down? I think "surface waves on an incompressible fluid in a gravitational field" are subtlely but importantly different than waves in an elastic material....

But think of a wave on a rope. Clearly the rope doesn't move left or right, but the wave propagates. Here the wave is transmitted via tension in the rope. Water doesn't really have 'tension'... ?

[kaolinfire.livejournal.com]

good point. I really wasn't making the incompressible connection.