12 ms·

that's insane! What is the speed its going?

lucb1e 2y ago
TL;DR some 200 km/h The article says some 20 km/s, but that's its speed in space. The video is crap (just repeats the same footage four times, no slow motion) but downloading that m3u8 with yt-dlp and running it frame by frame in mpv: it shows up on one frame (well, two because it does interlacing) and then there's already a dust plume. The camera looks pretty high up, maybe 3 meters? With it first appearing roughly in front of the camera (vertically), that would mean a lower bound of 3 meters in 1/30th of a second, or 1/15th if this interlacing makes it 15fps in reality which I suspect, meaning somewhere north of 324 or 162 km/h in either scenario It looks like a decent-sized stone to me on that one frame, maybe the size of one's hand? Call it a 15cm sphere for simplicity, WolframAlpha says that has a 177 cm² cross-section and https://www.omnicalculator.com/construction/stone https://www.omnicalculator.com/construction/stone comes up with a few kilograms (4-8) depending on the type of rock, with which we can fill in a terminal velocity calculator https://www.omnicalculator.com/physics/terminal-velocity https://www.omnicalculator.com/physics/terminal-velocity to get an estimate of 320 to 450 km/h depending on its weight (probably towards the higher end given that it's metallic) -- assuming we got the size anywhere near correct, of course Edit: someone posted (https://news.ycombinator.com/item?id=42822256 https://news.ycombinator.com/item?id=42822256) a YouTube link where it's visible for 2 frames! (I'll call them frame 1, 2, and plume.) Now the prize question is how far up it was in the first frame and what angle it comes in at. The biggest chunk looks to be about the same size in both frames, at least to within video compression artifacts, so that doesn't help figure out the angle. It also travels nearly twice the distance in pixels between frame 2 and plume as compared to frames 1 and 2, which would be an angle thing or a video compression thing. I don't see an interlacing effect in frame 2 anymore, and frame 1 is duplicated (the youtube video runs at 24 fps). I think this has passed through too many compression / re-encoding layers to say anything useful sadly. For the heck of it: say that it was 5 meters up in frame 1 and it takes 2/24ths of a second to traverse that, that would be 216 km/h Loading the audio tracks into Audacity, the YouTube version shows nothing until ~180ms before impact if I'm being generous, whereas the CNN version contains inaudibly faint noise starting around ~350ms before (don't know that that's attributable to the meteorite, but at least there's data instead of a flat line), which I guess tells us that CNN's version has undergone fewer recompressions. Sadly, I don't think there's enough samples to measure the doppler effect, also given that it's not going directly towards/away from us (the shift is more like 60° probably?). Three meters are traversed in 24ms at 450km/h, and while there's audible noise on both YT and CNN for ~85ms before impact, the spectra are just too noisy for me to make it out. Someone more experienced with measuring dopplers could have a stab at it, though More editing: it is only now that I properly read the article (I know, shame on me, I guess DIY is more fun) and it says a "professor of Earth and atmospheric sciences at the University of Alberta" also tried this approach but hasn't figured it out yet: '“We are working on analyzing the video to see if we can say more about the meteorite’s fall — including speed,” Herd said.' I'm curious if we can figure this out by dropping rocks at different speeds until we get a plume that expands as fast as this one (since we have enough footage to reliably see that) and leaves a similar-sized mark Final edit, another source someone posted (https://news.ycombinator.com/item?id=42822765 https://news.ycombinator.com/item?id=42822765) includes: "He said the rock that struck at Velaidum's home was probably travelling at least 200 km/h by the time it made impact." The news report video in that source also includes a picture of the pavement after cleaning up the dust, showing marks of some 3cm on the ruler included in the shot. Doing the same terminal velocity calculator as mentioned earlier, a dense type of stone of 3cm would be slowed to 196 km/h by our atmosphere
- NotYourLawyer 2y ago
  If we know its rough size, should be easy to figure out its terminal velocity. It’s just a rock.
  - lucb1e 2y ago
    Yeah, that's in the second paragraph

TL;DR some 200 km/h The article says some 20 km/s, but that's its speed in space. The video is crap (just repeats the same footage four times, no slow motion) but downloading that m3u8 with yt-dlp and running it frame by frame in mpv: it shows up on one frame (well, two because it does interlacing) and then there's already a dust plume. The camera looks pretty high up, maybe 3 meters? With it first appearing roughly in front of the camera (vertically), that would mean a lower bound of 3 meters in 1/30th of a second, or 1/15th if this interlacing makes it 15fps in reality which I suspect, meaning somewhere north of 324 or 162 km/h in either scenario It looks like a decent-sized stone to me on that one frame, maybe the size of one's hand? Call it a 15cm sphere for simplicity, WolframAlpha says that has a 177 cm² cross-section and https://www.omnicalculator.com/construction/stone https://www.omnicalculator.com/construction/stone comes up with a few kilograms (4-8) depending on the type of rock, with which we can fill in a terminal velocity calculator https://www.omnicalculator.com/physics/terminal-velocity https://www.omnicalculator.com/physics/terminal-velocity to get an estimate of 320 to 450 km/h depending on its weight (probably towards the higher end given that it's metallic) -- assuming we got the size anywhere near correct, of course Edit: someone posted (https://news.ycombinator.com/item?id=42822256 https://news.ycombinator.com/item?id=42822256) a YouTube link where it's visible for 2 frames! (I'll call them frame 1, 2, and plume.) Now the prize question is how far up it was in the first frame and what angle it comes in at. The biggest chunk looks to be about the same size in both frames, at least to within video compression artifacts, so that doesn't help figure out the angle. It also travels nearly twice the distance in pixels between frame 2 and plume as compared to frames 1 and 2, which would be an angle thing or a video compression thing. I don't see an interlacing effect in frame 2 anymore, and frame 1 is duplicated (the youtube video runs at 24 fps). I think this has passed through too many compression / re-encoding layers to say anything useful sadly. For the heck of it: say that it was 5 meters up in frame 1 and it takes 2/24ths of a second to traverse that, that would be 216 km/h Loading the audio tracks into Audacity, the YouTube version shows nothing until ~180ms before impact if I'm being generous, whereas the CNN version contains inaudibly faint noise starting around ~350ms before (don't know that that's attributable to the meteorite, but at least there's data instead of a flat line), which I guess tells us that CNN's version has undergone fewer recompressions. Sadly, I don't think there's enough samples to measure the doppler effect, also given that it's not going directly towards/away from us (the shift is more like 60° probably?). Three meters are traversed in 24ms at 450km/h, and while there's audible noise on both YT and CNN for ~85ms before impact, the spectra are just too noisy for me to make it out. Someone more experienced with measuring dopplers could have a stab at it, though More editing: it is only now that I properly read the article (I know, shame on me, I guess DIY is more fun) and it says a "professor of Earth and atmospheric sciences at the University of Alberta" also tried this approach but hasn't figured it out yet: '“We are working on analyzing the video to see if we can say more about the meteorite’s fall — including speed,” Herd said.' I'm curious if we can figure this out by dropping rocks at different speeds until we get a plume that expands as fast as this one (since we have enough footage to reliably see that) and leaves a similar-sized mark Final edit, another source someone posted (https://news.ycombinator.com/item?id=42822765 https://news.ycombinator.com/item?id=42822765) includes: "He said the rock that struck at Velaidum's home was probably travelling at least 200 km/h by the time it made impact." The news report video in that source also includes a picture of the pavement after cleaning up the dust, showing marks of some 3cm on the ruler included in the shot. Doing the same terminal velocity calculator as mentioned earlier, a dense type of stone of 3cm would be slowed to 196 km/h by our atmosphere

NotYourLawyer 2y ago
If we know its rough size, should be easy to figure out its terminal velocity. It’s just a rock.
- lucb1e 2y ago
  Yeah, that's in the second paragraph