![]() This person was better known for studying snowflakes, and is featured in a children's book called "Snowflake Bentley."His name was Wilson Alwyn Bentley, and he lived during the years after the Civil War. But my favorite story is that the very first person go get the idea of studying raindrops and their size distribution (which might lead to shape) before high speed camera. The advent of the high speed camera has allowed us to really study fluid movement at such high rates of descent. Of course a lot of interesting science went into learning about raindrop shape. Kulkarni and PE Sojka, AIP Physics of Fluids, 2014). Images of water droplets breaking under a constant air stream (Photo: V. If you want to know more you can read the paper by Emmanuel Vilermaux in the Journal Nature. This air pressure differential is what gives the larger droplet its jellyfish shape. Illustration of the air pressure forces that form a rain droplet (Photo: James E. It has to do with the falling droplet forming a high pressure of air below it as it falls, which creates a low pressure of turbulent air on top of it. There is some fun geeky weather stuff that goes with all this, especially concerning the amount of air pressure around the large droplet. Image of a raindrop falling, Emmanuel Villermaux (Photo: Live Science) Eventually, when it reaches 4.5-5 mm in size the cohesive molecular bonds of the water molecules can't hold the droplet together anymore, and the droplet simply bursts into smaller round droplets. As it goes down it becomes more and more convex (like a contact lens or thin plastic bag). This droplet will keep descending downward, flattening somewhat. The droplet forms into something that looks like a jellyfish bell without the tentacles, and it has a slight dimple in the middle of its underside. This is because the drop is heavier and it begins to be influenced more by air pressure pushing up as the droplet begins to sink down. Any time that this airborne droplet starts to join up with other droplets, and it gets bigger than 2 mm, then it starts to take another shape. When the drop grows, things get interesting. This is sort of like an airborne blob eating up Manhattan. They are round because of the covalent properties of water.Īs that raindrop starts to move around, it becomes more heavy and saturated, absorbing other droplets of water. These droplets are perfectly round or spherical, not teardrop shaped. Water droplets condensing and forming in clouds (Photo: Wiki Commons)Īs the water molecules start to condense and cool around the nuclei they begin to form a water droplet that continues to floats along in the atmosphere. They're about 1/100 of a millimeter in size, very tiny wee things. Nuclei can be anything from pollen or ash to fine grained sand. These are called nuclei, or condensed cloud nuclei (CCN). Now they can't just square dance together as water molecules and "ta-da" you have a raindrop, nope, you have to have dust or particulates for them to form around. When this happens the water molecules in the vapor start to condense. Cool air can't hold as much moisture as warm air, there just isn't enough energy, and the vapor becomes sluggish and heavy. The water vapor is warm and bouncing around quite happily, but as the water molecules rise into the the water vapor begins to cool in the atmosphere. As the Earth is warmed the water vapor rises on a mass of warm air that lifts skyward. We can't see it, but it's there (hot and humid days demonstrate this quite well). You know that the air is filled with water vapor, which is essentially a lot of water in gaseous form floating around us. Let's take a short cloud journey to discover the shape of raindrops. Raindrops form high up in the clouds, under pressure from air, changing temperatures, cooling, and gravity. Teardrops and faucet drips often fall from a short distance and they sometimes drizzle down a surface. The way teardrops and faucet drips form is very different from how raindrops form, though some of the molecular principles are the same. ![]() A very wrong, but frequently used, drawing of the shape of a raindrop (Image: Wiki Commons). However, those drawings are perpetuating a very common misconception, that raindrops are shaped like a teardrop. How many times have you seen a drawing of a raindrop as something that looks like a drip from a faucet? It's a common symbol that can be found everywhere, from children's books to lawn and garden logos. ![]() The Mystery of the Shape of Raindrops Raindrops on a window (Photo: Pixaby)
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