Ripples

[Head Teacher]

No matter what shape an object is why do the ripples form circles when you drop it in water?

[JustSia]

I would think that each point of an object would start a wave. These waves would radiate out and interfere with one another cancelling each other out and forming the usual ripple effect.

S.

[gen2]

JustSia is correct in saying every point creates a ripple and there is both constructive and destructive interference between the waves, but there is something else to consider.

The waves travel outwards with constant velocity. Let's say you throw in an oval stone 10 cm by 5 cm. Some of the wave front will start out 5 cm ahead of some of the others. This difference will remain constant. By the time the ripples have spread to a metre or so radius, the eye won't notice that 5 cm difference, particularly as it will usually be viewed from an oblique angle and look like an ellipse anyway.

[heathfield]

Gen2's answer can be observed if you drop a large barbell-shaped object into water. The ripples won't be circular.

[Geo1000]

The devasting Tsunami of last year is a classic case of the ripples not always being circular. The disturbance was a long fault line which started a wave crossing the ocean that was almost straight.

It was curved at the edges. If such a wave occured on an infinitely large ocean then eventually it too would look circular.

[Head Teacher]

Thanks for your answers. I need to try and explain this to some primary school children and they need a lot of convincing so wish me luck!