Shape of Droplets


Why do droplets adapt a round shape whenever it reaches the surface? Why not edged shapes?

In: Physics

The molecules of water (or other liquids) attract each other, which is why it’s a liquid and not a gas (where the molecules disperse to occupy the entire volume of the room available to them). They basically stick to each other. So this stickiness causes [surface tension](; the molecules in a glop of liquid will try to stick together as closely as possible.

And the shape with the biggest volume (inside) but the smallest surface is a sphere. The wiki article explains the forces that act to “pull the edges in” to form a sphere.

It has to do with the shape and properties of water molecules. So water is a “bent” molecule. We know it as H2O, 2 hydrogen atoms and 1 oxygen atom, but it’s easier to think of it as HOH;

Without getting too much into it, all the atoms want 8 electrons, but none of them have 8 alone – O has 6 and each H has 1. You can think of how many each has as how “strong” they are. They all share the electrons, so they each kind-of have 8, but the O is stronger and a bit greedy, so it keeps the electrons closer to itself than the Hs can. What this does is make the O a little bit more negatively charged, and the Hs a little more positively charged. Then, again because of where the electrons are, the Hs get crowded to one side a bit, therefore the water molecule looks like a ^ with the O at the top and an H at either bottom point, and since there is a charge difference (-O,+H), the molecule functions like a weak little magnet.

Now imagine a whole bunch of water molecules. Since they’re all like weak little magnets, they all want to line up; opposites attract so the slightly positive Hs are attracted to the slightly negative Os. This makes water “sticky.” Water is attracted to itself, a property we call *cohesion*. What this does is make water molecules always try to pull the selves into the center of any body of water, and just like we see with planets forming under gravitational force, this will always make a round shape.

Fun fact, it is this same “bent” shape of water that is responsible for the solid H2O, which we know as ice, floating on top of the liquid H2O; an uncommon property.

Edit: I realized after posting that you had a non-specific question of liquids, not water. Insofar as other liquids forming non-geometrical shapes, I think that mostly has to do with randomness of distribution. The best answer i can come up with is nothing *makes* them into geometric shapes. Those don’t really occur by accident