# Ripples in the water

1. Dec 9, 2006

### boredooom

Can someone give me a basic-ish explanation of why ripples are formed in the water when for example you throw a pebble in a lake or something?

Thanks

2. Dec 9, 2006

### marlon

You need three basic ingredients

1) a piece of matter (ie the water) that has some kind of elasticity (cohesion between the water molecules) in an equilibrium state

2) a source of energy that that will destroy that equilibrium state (ie the stone that you throw which distrubs the equilibrium state)

3) gravity acting as the force that tries to restore the equilibrium level

2) and 3) are two CONFLICTING phenomena which give rise to a periodic wavelike motion of the water: ie the ripples that you see.

More here : http://hyperphysics.phy-astr.gsu.edu/hbase/sound/wavplt.html#c3

marlon

3. Dec 9, 2006

### billiards

uhhh... ripples dude, they're like surface waves. ya know when ya get a kind of retrograde particle movement. ughhh??

are you saying why are they periodic? hmmmm... good question, probly coz the disturbance is ummmm vck?

4. Dec 10, 2006

### arildno

As for RIPPLES, we should probably add SURFACE TENSION as yet another restoring force besides gravity that might be relevant. For waves with larger wave-lengths, we may ignore the surface tension, but ripples have fairly short wave lengths.

5. Dec 10, 2006

### FredGarvin

You can also think of the peridicity as a resultant of the medium that is being disturbed wishing to return back to it's undisturbed state. When you throw a stone into the water, the water is disturbed by the addition of energy. That energuy goes into making a wave. The water has resisitive forces which try to balance the added energy.

6. Dec 10, 2006

### billiards

Actually the surface waves on water are kind of different from surface waves on land aren't they? On water they are evenly spaced because the surface is bobbing up and down periodically as a result of the initial disturbance which spreads out carrying information/energy in a big circle. I'd imagine that the surface tension is very important here.

On land the surface waves are caused by supercritical incoming seismic waves which combine and move along at a group velocity. I was thinking they were probably the same as ripples in some way, but of course s-waves can't travel in a fluid and ripples as far as I am aware are not associated with any strain, just particle displacement.