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Tired Again. But This Time Including 18th C. Science. A brick fell off my roof. Flapping was audible from indoors. With the aid of tramadol, I dragged myself back up on the roof, where I saw that the western edge of one sheet of plastic was lifted up, flopped over, and flapping -- and the ballast that had been on that part had either gotten nudged to the middle or rolled partway down the roof. While I watched, more of it slipped out from under its ballast. I hauled more brick-pieces up (this time I'd brought an extra rope to avoid dragging the bucket o' bricks up the ladder, but it was too heavy for me to trust myself to haul it all the way up from the ground so I carried it up the stair part of the fire escape and used the rope to get it the last stage. The owner of one or more of the vacant houses pulled up as I was going up the fire escape. Getting out of his car he drew his cell phone. I paused and looked his way, and he said, "Who are you?". I explained the situation and he said, "I guess that's all right then," and put away his phone. When I came back down his tone had shifted all the way over to friendly. (And in between, on one of my brickbucketfilling trips, he confirmed that the broken bricks I'd guessed were trash are in fact trash.) He was working on his windows while I worked on my roof. I need about another bucket and a half of ballast up there to comfortably handle the wind we have right now. I stood around watching the ... doggone it, I can never keep straight which one gets Bernoulli's name attached and which gets Venturi's -- I hate forgetting stuff like that ... ah, the narrow part of a carbeurator is the 'Venturi throat', right? So the Bernoulli principle must be what I'm thinking of ... Bernoulli effect working against me. I managed to get it so that no wind was blowing up under the plastic, but the wind blowing across the surface still tried to suck the plastic upward. As a bubble formed, the raised section started acting like an aerofoil, thus increasing the speed of the air across it and increasing the Bernoulli effect thereby. So enough force to get a wee bubble that nudges the ballast slowly as it ripples, becomes over several minutes enough force to start the edge of the plastic creeping out from under the bits of ballast right at the edge (the bits keeping the wind from being able to blow under the plastic). Exactly as I'd been afraid would happen. But standing on the roof instead of running the simulation in my head, I got to watch the process unfold. A much brighter image (because for some reason it was dusk in my mental simulation). Anywho, I drew the plastic as snug as I could, to minimize the amount the wind could bow it up to begin with, and stuck bits o' brick everywhere a bubble started to form until I got to the end of the second bucket, and by then I was feeling that even with the painkiller enabling me to be up there instead of moaning in bed, if I hauled one more bucketful of bricks up there then I'd lack the strength to get back down safely. So I'm done for today, crossing my fingers holding my breath knocking on wood and praying it doesn't tear loose before the wind slacks off, and dreading how much I'm going to hurt tomorrow compared to the already bad-enough-to-wake-me-up pain of this morning. I'll try to nap, and hope I'm able to lift the double bass into Breno's car to go to 3LF tonight. It's too windy to work solo with a sheet of plastic that's not already held down on a couple of edges, so I'll wait for calm before trying to attach the next sheet. I did take a few minutes to stand atop the chimney for a bunch of snapshots with the digicam. (I should drag the tripod and a film camera up there at some point, but not today.) One really feels the strength of each gust, on such a small perch. When the dripping started last night, quite some time after the rain got more serious than a sprinkle, it was noisy but ultimately totalled maybe a half gallon. I'm guessing that that was just after the top sheet of plastic shifted enough to expose the uphill edge of the second sheet. Last night's rain was nowhere near as heavy as that last storm that kept me up all night, but during that one I was seeing in excess of eight gallons per hour pouring through the ceiling. Methinks the plastic is helping. And now it's time to waken the cat, who finally stopped pestering me for having left her alone for an hour or two (oh, the horror, the poor neglected kitty!) and fell asleep on my lap while I wrote this. But I need me some lunch, and I have to check on the laundry, before I too fall asleep. Finally, as I mentioned in a comment elsewhere, if I had to spend a night without power during a February when I'm relying on electric space heaters for warmth, I suppose the night leading into the absurdly unseasonably warm day was the night to do so. By the time my electricity came back on it was warmer outdoors than in any but the warmest room in my house. |
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