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I always thought that raindrops look like this emoji 💧. But today, I shot it in slow-mo (see on YouTube), and they look more like sticks.

Was it some light effect of my camera, or do they really look like that? And if it's the real deal, why do they look like that?


Edit: I found another video that I took from that rain. I didn't see it at first, but after looking again, it shows rain drops as little balls.

I took the videos 10 min apart. The second video(with balls) is when the rain just started.

Why does the rain look like sticks in one video and like balls in another? I used the same camera to record it.

enter image description here Screenshot at 00:00:18

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  • $\begingroup$ jstor.org/stable/24944469 $\endgroup$ Aug 8, 2022 at 7:32
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    $\begingroup$ This might be a better question for the Photography SE. $\endgroup$
    – Drake P
    Aug 8, 2022 at 14:14
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    $\begingroup$ youtube.com/watch?v=6G6omXLTAj0 $\endgroup$ Aug 8, 2022 at 14:15
  • $\begingroup$ see this video of raindrops falling, they are streaks,, exxcept the ones slow enough while bouncing off the leaves , where they are white dots videvo.net/video/close-up-shot-rain-drops-falling-on-leaves/… $\endgroup$
    – anna v
    Aug 8, 2022 at 18:55
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    $\begingroup$ Ultimately, it's just motion blur. When you look up, you get shorter streaks, especially higher in the frame. On top of that, who knows what the software in your camera is doing - it might be auto-adjusting various camera settings, and it might be interpolating the frames to make the video appear to have a higher framerate than it actually does. So the filming conditions may be different, even though it's the same camera. $\endgroup$ Aug 11, 2022 at 3:06

4 Answers 4

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Your shutter speed is too slow, and you are seeing the raindrops travel within each video frame. Falling raindrops are approximately spherical. The teardrop shape sometimes occurs in droplets moving across a surface, such as a raindrop on glass (or, I suppose, a teardrop on a person’s face).

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    $\begingroup$ The proof that they are usually highly spherical is the way the rainbow looks. An inclusion of a small non-sphericity leads to twinned rainbows. $\endgroup$
    – Ruslan
    Aug 8, 2022 at 15:41
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    $\begingroup$ Atmospheric Optics is one of the underappreciated gems of the Internet, and I'm just tickled pink that you linked to it before I did. Excellent point, @Ruslan. $\endgroup$
    – rob
    Aug 8, 2022 at 15:56
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    $\begingroup$ Ideally, this answer should be supplemented with footage that supports the physical theory with empirical evidence $\endgroup$ Aug 8, 2022 at 16:32
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    $\begingroup$ To put some numbers on it, a typical raindrop falling at its terminal velocity of 9m/s falls 15cm in one frame of a 60fps video, which seems fairly consistent with the OP's video. $\endgroup$ Aug 8, 2022 at 19:30
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    $\begingroup$ @JThomas that's unlikely: tiny droplets would result in fogbow instead of rainbow. Besides, twinned rainbow is not a frequent phenomenon, while normal rainbow is, while the rain usually does fall :) $\endgroup$
    – Ruslan
    Aug 8, 2022 at 19:43
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Small raindrops are roughly spherical. As they get larger, they flatten (see figure).

enter image description here

Even larger raindrops are unstable, and break up:

enter image description here

(figures from https://gpm.nasa.gov/education/articles/shape-of-a-raindrop).

For spherical rain drops, Mie theory is used for computing a radar cross section (measured in dBZ, which is a log-10 scale of $10\times\ {\rm mm^6/m^3}$, one of the strangest units in science, IMHO). The larger drops' asymmetric shape can be retrieved by comparing horizontal and vertical radar cross sections.

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    $\begingroup$ I doubt that this exact case is related to large raindrop size, because in video it is seen like vertical sticks, while when large raindrop is about to divide - it becomes like a "hantel",- i.e. horizontal stick. So OP's noticed phenomena can't be related to overgrowing raindrops. $\endgroup$ Aug 8, 2022 at 13:29
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    $\begingroup$ Way back when I was an undergrad, and this book (books.google.com/books/about/…) was in its first edition (late 70s), I took a "Particulate Systems" class from one of the authors (Grace). It definitely included high speed photos of falling water droplets looking either spherical, hamburger bun shaped or nearly red-blood-cell shape depending on their size (just like the nasa.gov illustration) $\endgroup$
    – Flydog57
    Aug 8, 2022 at 16:26
  • $\begingroup$ Why is the reflectivity of spherical rain droplets proportional to the sixth power of their diameter anyway? It seems that fact explains the mm^6 unit, but I can't find any references online as to where that relationship comes from. $\endgroup$
    – jogloran
    Aug 10, 2022 at 5:32
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    $\begingroup$ @jogloran en.wikipedia.org/wiki/… $\endgroup$
    – JEB
    Aug 10, 2022 at 12:44
  • $\begingroup$ @JEB I updated the question, please review $\endgroup$ Aug 10, 2022 at 14:35
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Photographic sensor, camera sensor, film... all integrate the light received during the exposure time. The brightness and color of each pixel depends on the sum of all the light received during the exposure. So if an object moves during the exposure, it will look blurred, like this car. The background is stationary, so it is not blurred.

enter image description here

This is called "motion blur". The amount depends on how far it moves during the exposure. If it doesn't move more than one pixel, then the photo will be very sharp. Playing with the shutter time setting on the camera can give completely different results. On the left, a short exposure time "freezes" the subject. On the left, a long exposure time turns every drop into a long streak, for a more artistic look.

enter image description here

The video you show was shot with a rather long exposure time, which means the drops are affected by motion blur, and they look like streaks. Here's a picture of water drops shot with a short exposure time:

enter image description here

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  • $\begingroup$ I updated the question. Please review. $\endgroup$ Aug 10, 2022 at 14:36
  • $\begingroup$ It looks different because the camera will automatically adjust exposure time depending on ambient light conditions, so the picture is exposed correctly. Unless you set everything to manual (if it even has a manual mode). $\endgroup$
    – bobflux
    Aug 10, 2022 at 14:38
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When I look at individual frames, raindrops look like little white lines about 10 to 20 times as long as they're wide. I think that's how far they fall while one frame is being taken. Maybe some of them are farther away than others, and that makes the length difference.

If you see a series of frames like that, they're going to look like long lines.

I thought while looking at it that some particularly bright ones looked more like sticks than the others, but I didn't find the frames they were in. Maybe they were bright because they were closer, so they were just longer and wider lines.

But I'd consider the possibility that maybe sometimes you get something that isn't an individual raindrop. Imagine you were in a small airplane and you poured a cup of water. Air resistance would quickly spread it out. But maybe some of it would tend to stay together some. You could get some big blobs that followed each other, the leader breaking up the air resistance some for later ones?

So you might see something that wasn't just a random raindrop, but something more, that lasted longer, that your eye might connect?

I can imagine it, but I didn't look long enough to see whether it was there. enter image description here

The experimental evidence supports JEBs claims. With a vertical wind tunnel blowing fast enough to keep water droplets stationary, they make the shapes he describes. You can see it for yourself.

video of falling water droplets

So if inside real clouds, the only forces involved are gravity, air pressure, and surface tension, and the water droplets don't interact with each other, then these are the only shapes they'll have.

The only other force that I know is involved is electric charge, and I'd expect that to be mostly inside the clouds and not for large raindrops on the way down. And I can't think of any interactions that would make a difference. So my guess is that those are the shapes. Though there could be something I haven't thought of.

I remember looking at thick shampoo in transparent bottles. I'd turn them over and air bubbles would travel to the top in raindrop shapes. That's because the air bubbles didn't have much surface tension at all. Water has so much surface tension that you won't see a raindrop tail.

The earlier video is different.

higher second third fourth next higher fifth

It's like with the other one it did slow scans, and this time it does quick scans that sometimes record the same raindrop in two places.

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  • $\begingroup$ That is just light filtering through leaves and branches . the ones onth reight are reflections from the windows of the building. $\endgroup$
    – anna v
    Aug 8, 2022 at 13:33
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    $\begingroup$ Upvoted for circling the raindrops in the video still. However, the “big blob” suggestion is incorrect. To get an idea why, take a stroll across a tall bridge near you, empty your water bottle off the side, and watch how the water breaks up into droplets. To answer the question “what about more water,” plan a hike to a waterfall, and watch how that stream breaks up. $\endgroup$
    – rob
    Aug 8, 2022 at 14:53
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    $\begingroup$ have deleted my answer , because after looking again with print screen I think the white dots are light coming through the leaves and branches, It needs more sophisticated tools to manipulate the video, or if the streaks you point out are drops, it needs a faster camera to see the drops.. $\endgroup$
    – anna v
    Aug 8, 2022 at 18:31
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    $\begingroup$ look at this videvo.net/video/close-up-shot-rain-drops-falling-on-leaves/… . the camera is not fast enough, except for the bouncing drops on the leaves which are slower $\endgroup$
    – anna v
    Aug 8, 2022 at 19:13
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    $\begingroup$ It's the same effect that makes the wheel on this famous old photo of a racecar elliptical rather than circular. The car has moved forward between when the bottom of the wheel was exposed and the top. $\endgroup$ Aug 9, 2022 at 16:48

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