Post by thread:[OT]: 127 1 sq. ft. mirrors set a wooden boat on f

Archimedes was not joking. Found via Slashdot. This seems to be a step in the right direction wrt. (non)steam powered solar generation. 1100 deg. F is ~590 deg. C, ~860 K and ~2.6 bars of air pressure in 'my' turbo system. 127 square feet of mirrors are ~11 square meters (11 kW in the full sun). Their target (illuminated area) seems to be about 4-5 square feet (~0.5 sq. meters, from the photos) for a gain of ~25:1. I think that they put about 5kW into that 0.5 sq. meter with losses. I am surprised that such a high temperature could be reached in open air (without a baffle or shield). I suppose that the charcoal formed a porous surface that was both a blackbody and a shield against convection. This is a good lesson ;-) Blackened (smoked) steel wool looks good as 'blackbody' for the turbine experiments ;-) http://web.mit.edu/2.009/www/lectures/10_ArchimedesResult.html Peter

> > Archimedes was not joking. Found via Slashdot. This seems to be a step > in the right direction wrt. (non)steam powered solar generation. 1100 > deg. F is ~590 deg. C, ~860 K and ~2.6 bars of air pressure in 'my' > turbo system. 127 square feet of mirrors are ~11 square meters (11 kW in > the full sun). Their target (illuminated area) seems to be about 4-5 > square feet (~0.5 sq. meters, from the photos) for a gain of ~25:1. I > think that they put about 5kW into that 0.5 sq. meter with losses. > > I am surprised that such a high temperature could be reached in open air > (without a baffle or shield). I suppose that the charcoal formed a > porous surface that was both a blackbody and a shield against > convection. This is a good lesson ;-) Blackened (smoked) steel wool > looks good as 'blackbody' for the turbine experiments ;-) > > http://web.mit.edu/2.009/www/lectures/10_ArchimedesResult.html They did this because Mythbusters tried it, and couldn't get it to work. The boat got a bit warm. Slashdot has an update where Discovery Channel (produces Mythbusters) invited MIT to have a go where they failed. Didn't work. No word on Round 3. Tony

> > web.mit.edu/2.009/www/lectures/10_ArchimedesResult.html > > They did this because Mythbusters tried it, and couldn't > get it to work. The boat got a bit warm. So how does that affect Mythbusters' credibility ? I'm sure if they'd actually tried cedar/wax instead of oak it would've gone up a lot quicker, and probably with fewer mirrors. I saw the builders next door putting cedar scraps on their bonfire. Talk about flammable, went up like cardboard. So although their experiment worked they might have done it the hard way > Slashdot has an update where Discovery Channel (produces > Mythbusters) invited MIT to have a go where they failed. > > Didn't work. But the class above is from MIT ?

> > They did this because Mythbusters tried it, and couldn't > > get it to work. The boat got a bit warm. > > So how does that affect Mythbusters' credibility ? > It doesn't, they didn't have any to start with :-) Anybody whose seen steel melted with a solar furnace (~40 inch fresnel lens) knows this is only a matter of focus. Wether Archimedies did it or not is a question for historians to debate, but the possibility is evident to any 10-year old kid with a magnifing glass and an ant hill. -Denny

> So how does that affect Mythbusters' credibility ? It busts their sense of logic. The fact that they could not reproduce the effect does of course not prove that it is not possible, just that it is not possible with the exact setup they used. Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products docent Hogeschool van Utrecht: http://www.voti.nl/hvu

> > So how does that affect Mythbusters' credibility ? > > It busts their sense of logic. The fact that they could not reproduce > the effect does of course not prove that it is not possible, just that > it is not possible with the exact setup they used. Ayup. Let's not have another Mythbusters knock-down dragout, okay? It's just entertainment and NOT SCIENTIFIC. After all, science is composed of things which can be conclusively disproven, but can never be conclusively proven. Mike H.

> > It busts their sense of logic. The fact that they could not > reproduce > > the effect does of course not prove that it is not > possible, just that > > it is not possible with the exact setup they used. > > Ayup. Let's not have another Mythbusters knock-down dragout, > okay? It's just entertainment and NOT SCIENTIFIC. OK, read my post as "It busts *only* their sense of logic." and let me add a belated smiley. :) Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products docent Hogeschool van Utrecht: http://www.voti.nl/hvu

{Quote hidden}> > > web.mit.edu/2.009/www/lectures/10_ArchimedesResult.html > > > > They did this because Mythbusters tried it, and couldn't > > get it to work. The boat got a bit warm. > > So how does that affect Mythbusters' credibility ? > > I'm sure if they'd actually tried cedar/wax instead of oak > it would've gone up a lot quicker, and probably with > fewer mirrors. I saw the builders next door putting cedar > scraps on their bonfire. Talk about flammable, went up > like cardboard. So although their experiment worked they > might have done it the hard way > > > Slashdot has an update where Discovery Channel (produces > > Mythbusters) invited MIT to have a go where they failed. > > > > Didn't work. > > But the class above is from MIT ? Mythbusters made a large disc, and covered it with mirrors. Apparently that was how Archimedes did it. They couldn't get the focus tight enough. From what I can remember, their model boat was made out of some sort of pine, then covered in tar, etc. MIT lined up a bunch of mirrors in a row, and had to continually adjust them as the sun moved. Got the boat to burn eventually. Took 10 minutes. The update is here: http://science.slashdot.org/article.pl?sid=05/10/23/1349221&tid=14. Bit light on details of what the second MIT team did, but "mirrored system shaped like flower petals" sounds like what Mythbusters tried. There was a bloke in the '70s who set a boat on fire with mirrors, so it's not like it can't be done. Mythbusters' point was the Archimedes story was a myth. A big mirror makes a crap weapon, especially if you need to be in arrow range. Don't forget http://www.solardeathray.com. Tony

On Mon, 24 Oct 2005, Tony Smith wrote: > They did this because Mythbusters tried it, and couldn't get it to work. > The boat got a bit warm. > > Slashdot has an update where Discovery Channel (produces Mythbusters) > invited MIT to have a go where they failed. > > Didn't work. > > No word on Round 3. About Mythbusters I don't really know or care. This is interesting to me only from the point of view of its demonstration of the feasability of high enough temperatures with simple mirrors in the sun, and without a fancy receiver. Peter

> After all, science is composed of things which can be conclusively > disproven, but can never be conclusively proven. Naughty Mike! Fancy bringing up religion again!!! Such dangerous and heretical concepts must be nipped in the bud lest they burst forth in a conflagration that will deluge the earth. [Google knows]. Don't you know that such nasty biased assertions are banned on PICLIST ??? ! The cheek of, even ever so obliquely, hinting that there is "real science" and 'hard science' versus various other sorts. The utter nerve of bringing up the verboten issue of falsifiability. You should be ashamed! :-) Keep up the good work. Heresy will yet win the day. Popper rulez !!!!!! R '3 cheers for hard Science' M

The only mirrors Archimedes had were front surface (polished metal). Rear surface mirrors didn't appear until the 16th century (tin mercury amalgam) and silver deposition wasn't invented until 1835. Dave Tony Smith wrote: >Only 3 problems with front surface mirrors - expensive, hard to get, and I don't think Archimedes had any. > >Tony. > >(flat front surface mirrors are used in kaleidoscopes, if anyone was wondering) > > > > >>{Original Message removed}

Peter wrote: > On Wed, 26 Oct 2005, Tony Smith wrote: > >> Only 3 problems with front surface mirrors - expensive, hard to get, >> and I don't think Archimedes had any. > > > Make that two: he likely had ONLY front surface mirrors. Either > bronze, silver, or mercury polished copper. > > Peter I believe the siege mirrors were polished bronze. --Bob -- Note: To protect our network, attachments must be sent to spam_OUTattachTakeThisOuTengineer.cotse.net . 1-520-777-7606 USA/Canada http://beam.to/azengineer

I realize the legend suggests the boats were set afire, but I was thinking that might not be the most effective way to use a focused sunlight weapon. Wood requires temperatures of several hundred degrees to ignite, and being boats they would likely be wet (at least on the surface). But human flesh is much more sensitive. Severe pain and injury could be achieved at significantly lower temperatures than those needed to ignite wood. It seems that even 3-4 times normal sunlight would be enough to cause eye injury or at least temporary blindness, and would certainly be enough to prevent attackers from effectively targeting the defending troops. Thoughts? -Denny

> I realize the legend suggests the boats were set afire, but I was thinking > that might not be the most effective way to use a focused sunlight weapon. > > Wood requires temperatures of several hundred degrees to ignite, and being > boats they would likely be wet (at least on the surface). But human flesh > is > much more sensitive. Severe pain and injury could be achieved at > significantly lower temperatures than those needed to ignite wood. It > seems > that even 3-4 times normal sunlight would be enough to cause eye injury or > at least temporary blindness, and would certainly be enough to prevent > attackers from effectively targeting the defending troops. > > Thoughts? > > -Denny Sounds ok, but hard to do in practice. A scaled up version of kids frying ants with a magnifying glass? You need to focus on one person at a time, who'll be running around rather quickly (or hiding). Individual soldiers with polished shields wouldn't be co-ordinated enough, it's hard to see your "hot spot" in amongst the 100 or so others. A frame containing the mirrors is a bit large & heavy, so hard to swing around easily. Sure, you could hang it off some ropes, but then you also need to adjust the focus. I guess you could dazzle are few of them until their friends put a few arrows in you. The Romans always were sore losers. Tony

> Sounds ok, but hard to do in practice. A scaled up version > of kids frying ants with a magnifying glass ? Oh, is THAT what they're doing. I always thought they were just investigating the curious phenomenon of pismiral spontaneous combustion ;-) > You need to focus on one person at a time, who'll be running > around rather quickly You could always do the sails or ropes. Those old wooden ships would have had easily-ignitable tar/wax/oil. Not forgetting that the original ships were planked with cedar/cypress, which would go up a lot quicker than oak And no reason why some mirros couldn't be used to dazzle the Roman's archers ========================== I saw a documentary once in which they tried to re-construct a full-sized Archimedes Claw http://www.mlahanas.de/Greeks/Inventions.htm "others they lifted up into the air by an iron hand or beak like a crane's beak and, when they had drawn them up by the prow, and set them on end upon the poop, they plunged them to the bottom of the sea; or else the ships, drawn by engines within, and whirled about, were dashed against steep rocks that stood jutting out under the walls, with great destruction of the soldiers that were aboard them. A ship was frequently lifted up to a great height in the air (a dreadful thing to behold), and was rolled to and fro, and kept swinging, until the mariners were all thrown out, when at length it was dashed against the rocks, or let fall" It worked (within limits), but outrageously heavy, cumbersome and not very practical. Much more effective ways to attack a ship in harbour

It took MIT 10 minutes to set fire to a boat just sitting there. Maybe you could ask them to drop anchor while you got organised. Sounds like a Monty Python sketch. By that time the Romans would have swum ashore, taken a few photos, grabbed some souvenirs and made a few large holes in your body. Tony I saw that claw doco, can't say I was overly impressed. If you're in claw range, you might as well dump some burning oil or rocks on them. I guess you could throw bits of broken mirror at them too. Tony {Quote hidden}>> Sounds ok, but hard to do in practice. A scaled up version >> of kids frying ants with a magnifying glass ? > > Oh, is THAT what they're doing. I always thought they were > just investigating the curious phenomenon of pismiral spontaneous > combustion ;-) > >> You need to focus on one person at a time, who'll be running >> around rather quickly > > You could always do the sails or ropes. Those old wooden ships > would have had easily-ignitable tar/wax/oil. Not forgetting that > the original ships were planked with cedar/cypress, which would > go up a lot quicker than oak > > And no reason why some mirros couldn't be used to dazzle the > Roman's archers > > ========================== > > I saw a documentary once in which they tried to re-construct > a full-sized Archimedes Claw > > http://www.mlahanas.de/Greeks/Inventions.htm > > "others they lifted up into the air by an iron hand or beak like a > crane's beak and, when they had drawn them up by the prow, and > set them on end upon the poop, they plunged them to the bottom of > the sea; or else the ships, drawn by engines within, and whirled > about, were dashed against steep rocks that stood jutting out under > the walls, with great destruction of the soldiers that were aboard > them. A ship was frequently lifted up to a great height in the air (a > dreadful thing to behold), and was rolled to and fro, and kept > swinging, until the mariners were all thrown out, when at length it > was dashed against the rocks, or let fall" > > It worked (within limits), but outrageously heavy, cumbersome > and not very practical. Much more effective ways to attack a > ship in harbour > > -