I noticed about a year ago that rain falling on a puddle always formed circular rings. Does anyone know the specific reason for this? Also, are there any liquids that don't form circular rings when "rained" on?
As far as surface tension remains the dominant force, the ring formed by a drop impacting on a pool remains circular : this is simply due to surface minimisation of a free-surface shaping a constrained liquid volume.
You can obtain non-circular rings if the drop velocity at impact is high enough. Then, you may see an instability that induces a corrugation along the liquid ring (or rim). This is generally quantified by the Weber number, that compares the relative importance of inertia and surface tension forces.
Lauren,
Water has a very high surface tension.
A falling drop of water is essentially spherical (somewhat flattened on its underside for the very largest droplets).
It is not surprising that a spherical shape, striking a flat surface, would lead to a ring-like shape of ejecta.
Hi Lauren.
Rain that is not falling perpendicular to the surface of a puddle, for example, in a strong wind, produces non-circular patterns. It would make a great PhD research project to understand the relationships involved.
As far as surface tension remains the dominant force, the ring formed by a drop impacting on a pool remains circular : this is simply due to surface minimisation of a free-surface shaping a constrained liquid volume.
You can obtain non-circular rings if the drop velocity at impact is high enough. Then, you may see an instability that induces a corrugation along the liquid ring (or rim). This is generally quantified by the Weber number, that compares the relative importance of inertia and surface tension forces.
Sounds simple and amusing, in the world of Physics. Just a rain drop
@Ignatius Barasa.
Just a raindrop....perhaps. I see an under researched field of hydrodynamics.
Ian
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