Visualizing the R-value in yarn
December 3, 2020 7:14 PM   Subscribe

Want to see a crocheted illustration of the importance of reducing the R-value? Norwegian biostatistician Kathrine Frey Frøslie explains in this 4-minute video.
posted by Quietgal (19 comments total) 45 users marked this as a favorite
This is fantastic and also extremely distressing on multiple levels. Oh god, her poor hands.

Thanks for posting!
posted by brook horse at 7:34 PM on December 3, 2020 [6 favorites]

Truly - a mask in time saves nine...

An interesting visual representation of exponential growth - something that is truly counter intuitive when the 'compound interest rate' isn't a small fraction.
posted by mce at 8:05 PM on December 3, 2020 [3 favorites]

I love hyperbolic crochet! It’s very useful for explaining just this kind of thing, and it’s super squishy. It was great how she used red and yellow feathers in her setup explanation and followed that with alternating red and yellow stitches in her sample work. I wish she had also displayed the weight of each sample just to drive it home with some more numbers - the way she struggled to pick up the last one makes me want to know.

As for her hands, there are specific stretches for crocheters and different warm ups you can do. I try to remember them sometimes... I should be better at it. The ones that feel most effective for me are the praying hands thing where you put your palms flat together, and gently press your wrists inward while lifting your hands up and down, and simply bending each finger back and holding for ten seconds followed by pulling each finger across the palm for ten seconds. These seem to get all my trouble spots.

I wonder how you could make the worst case R=6 scenario. The stitches just wouldn’t fit into the space available so you’d have to do something like use smaller and smaller gauge fiber in each row, which removes the impact of the visualization, or build in spacing between each stitch on the earlier rows which means it won’t have much structure holding it together at all. It would also be so many stitches by the final row you’d end up using a king sized blanket’s worth of yarn.
posted by Mizu at 8:28 PM on December 3, 2020 [8 favorites]

This is brilliant.

And, as a fellow crocheter, my first thought on seeing R=2.5 was "oh, her poor hands". But I suppose it's not that tight, since for each stitch you're only adding 1.5 (so 25 stitches into 10). It looks worse because it's going up so fast.
posted by jb at 8:44 PM on December 3, 2020

Very disappointed... I thought this would be about R-value for insulation purposes.
posted by Ted Walther at 8:50 PM on December 3, 2020 [7 favorites]

I thought this would be about R-value for insulation purposes.

Those last two masses of convolutions looked like they'd be pretty warm if you filled your wall with them.
posted by eviemath at 9:04 PM on December 3, 2020 [5 favorites]

Truly - a mask in time saves nine...

With a retransmission rate of 1.4, a bad flu year’s rate, a chain of twelve personal contacts later - that is to say 1.4^12 - is about 60 infected people, in total.

3^12 - three being the COVID-19 retransmission rate, give or take - is half a million people. And back of the envelope, with about a 2% mortality rate: a mask in time saves easily north of nine thousand.
posted by mhoye at 9:32 PM on December 3, 2020

I love her dangling covid-19 pompoms! A-and here's the video in the original Norwegian
posted by chavenet at 12:41 AM on December 4, 2020

exponential growth - something that is truly counter intuitive when the 'compound interest rate' isn't a small fraction

1.2 is still a pretty small fraction compared to R=2.5, and that's still more than enough to get people into terrible trouble with snowballing credit card debt.
posted by flabdablet at 1:57 AM on December 4, 2020 [1 favorite]

Really nice way to show exponential growth.

Norwegian public health messaging and practice seems to be working pretty well, balancing advice with stricter measures brought in quite quickly when needed.

They've had around 350 deaths total since the pandemic began, which I believe is around 6.5 per 100k of population. That compares to their infamous neighbour, Sweden, who have had over 7000 deaths (around 68 per 100k). The US is at around 80 per 100k.

I've spent a lot of time in Norway this year and the restrictions have been much less onerous than in the UK.
posted by knapah at 2:33 AM on December 4, 2020

This lady seems knit together from strands of pure Celine Dion energy. What a biostatistical knitting muse she is.
posted by glasseyes at 7:13 AM on December 4, 2020

Instructions for the coropoms
posted by glasseyes at 7:15 AM on December 4, 2020 [1 favorite]

I can't imagine how much time and effort it would take, but having a knitting-based curriculum for all of STEM might be the coolest thing ever. This lady rocks!
posted by riverlife at 7:53 AM on December 4, 2020 [1 favorite]

What a biostatistical knitting muse she is.

having a knitting-based curriculum for all of STEM might be the coolest thing ever.

Craft pedants everywhere: it's crochet, not knitting.

(That said, the pompoms look like they are knitted - and you should be able to reproduce the R patches with knitting.)
posted by jb at 9:24 AM on December 4, 2020 [1 favorite]

The Home of Mathematical Knitting (includes links to crochet and other, and the three current books).

IME this kind of thing is spectacular for the few people who were already conversant with both domains, and has an occasional convert, but loses more students to confusion in one or the other, like writing assembly code on orchestral staves.
posted by clew at 10:30 AM on December 4, 2020 [2 favorites]

I suppose this is as good of a place to put as anywhere, but I've wondered if there is the relationship between the size of a ball (or cake) of yarn and the circumference of the ball's great sphere. Obviously, more stitches can be made from a single wrap from the outside of a large ball, but it seems like the balls shrink faster at the start then at the end? Since the home of mathematical knitting has spatial sculptures way more advanced than my thought experiment, it seems like this is a solved proof, but basic googling hasn't brought up anything useful. My conception is that you are converting 3-d space to 2-d, so there is an exponential element, but that's as far as I get. If other people have insights, I'd love to hear them!
posted by Hermeowne Grangepurr at 12:17 PM on December 4, 2020

Fantastic! Thanks!
posted by mazola at 12:51 PM on December 4, 2020

Hermeowne Grangepurr, the balls should shrink more slowly at the beginning than when small -- roughly calculating, thinking of a big ball of yarn of radius R, yarn that has diameter Y --

The surface area of the ball is 4πR². You can cover that surface area with a piece of yarn that's 4πR²/Y long. There are extra crossings in an actual ball, but also the yarn ball is lumpy not a perfect sphere, so call that the length. If you knit off that length of yarn, you've made the ball Y smaller in radius, one layer of yarn.

To make a smaller ball, radius r, smaller by one layer of yarn, you only need to knit 4πr²/Y of yarn. The ratio of layer-of-big-ball to layer-of-small-ball is R²/r², which is going to amplify the ratio of the ball sizes, R/r. It takes much less knitting to peel off a layer of the small ball.

(If it feels faster when starting, maybe that's the excitement of a new project. Think instead of the anxiety when you aren't done with the last sleeve but your last ball of the dyelot is shrinking, shrinking...)

Maybe we react emotionally to the rate of decrease of the ball? Like, how long it takes to make the radius 4/5 of what it was? This turns out to enough algebra to be annoying to read in text, but it cancels out even more dramatically -- if the small ball has a radius half the size of the big one, we can take off 1/5 of the small ball with an eighth as much knitting. (We just jumped to cubes instead of squares because I switched to thinking of ball volume -- when thinking of "a layer of yarn" the volume part was the thickness Y of the yarn times the area of the sphere.)
posted by clew at 6:00 PM on December 4, 2020 [1 favorite]

I hope she takes requests. I'd like to see the first five seconds of the Big Bang.
posted by storybored at 7:32 PM on December 4, 2020 [2 favorites]

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