Little ripples in water

[eyedea]

Why is it, that if you throw an object into a body of water the ripples always form a perfect circle every time?

[DPWhite]

Because the velocity of waves from a uniform source in a single medium is constant. In your case, water, presumably in the sink washing dishes or some such, it is about 30 centimeters a second if I recall my experiments in physics for water wave motion from 22 years ago. You would probably find that they a different velocity in a differing viscosity liquid like oil. Light waves, for example, travel slower through water than they do through air, which is slower than a vacuum.

[happyheathen]

how about:

"Ripples in still water...
When there is no pebble tossed,
No wind to blow..."

?

I know, GD...

[DPWhite]

Yeah, try dropping a pebble in a box of rain and watch the inverted circles bouncing back, it will roll away the dew...

[Mangetout]

Actually, if the water is in a very shallow tray with a sloping bottom (so that one side is shallower than the other) then the ripples will not form a perfect circle.

[femtosecond]

The speed of a wave on (ideal) water is the same in every direction. So in a given period of time a disturbance will spread over the same distance in every direction from its starting point. All points with the same distance to another point lie on a circle. That's a very fundamental law of nature. You can base many others on it, for instance that a light appears darker and darker if you move away from it.