To confirm the social-distance rule: If cough droplets are 0.1 mm and ejected at 10 m/s, a quick Stokes law calculation shows that they travel about 2m laterally and settle in about 1s. https://pbs.twimg.com/media/EUTjWTdWkAIQ73D?format=jpg … (chart courtesy of @DrPascalMeier).
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Replying to @gmusser @DrPascalMeier
I read that Japanese quarantine officials claimed that they got infected by Diamond Princess passengers from 2m distance while using droplet protection; there is possibly some slight airborne thing going on as well.
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Replying to @Plinz @DrPascalMeier
In this simple Stokes law calculation, the distance scales with 1/R², so larger droplets go farther (more inertia). So a lot depends on the size spectrum.
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Replying to @gmusser @DrPascalMeier
Of course if you are hit by larger gobs you are also more prone to notice. When small droplets evaporate before they hit the floor, the virus may stay in the air and waft around for a while.
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Also, Stokes's law assumes rigid spheres. Larger droplets may assume a more aerodynamic shape. Smaller ones may be carried further on air currents. I'd want to know more about both before relying heavily on the simple calculation if my life is on the line! (It may be—so I do!)
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Here’s a chart of the Stokes law calculation. Yes, Stokes law is an approximation and misses much. My main point, though, is that I think the 2m guideline is based on such a calculation, and it is very sensitive to assumptions about size and initial speed.pic.twitter.com/xCmTcebzJK
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It makes sense to think about why this is three times as infectious as the flu, and why infections over larger distances have been described.
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It could be aerosol transmission, or it could require fewer virus particles to produce an active infection, or it could be the length of time people run around infectious w/o symptoms (as in early measles + asymptomatic carriers).
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