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  • So there's been a new story going around the British media about a car melting in London, which apparently used you to its proximity to a new building, which is going up in London.

  • The physics is a thing called geometric optics, and this is about how you do with understanding how like propagates.

  • And if you really want to do the job properly, then you gotta solve Maxwell's equations and really so very complicated set of equations and lights actually quite complicated, but for many purposes you don't need to do that because essentially, the main thing that most people know about light is that it travels in straight lines.

  • So the story is that some guy just parked his car on the street, went away for now, came back and found that most of the plastic parts of his car and melted on.

  • There was actually a note, I think stuck under the windscreen, saying your your car's melted.

  • Please come and see us from the builders of this building, who clearly recognize that they're building had something to do with the fact that this car had been melted.

  • So it's a new building.

  • It's not even finished yet it's still going up.

  • And actually there had already been a few stories around about people being dazzled in the streets and so on.

  • So it was already people were starting to think there's something strange going on with this building, but this was kind of the the really extreme case of all the bad things that this building ended up doing.

  • I have a bit of history in this.

  • I've actually looked at the effects off large reflecting surfaces on that the way they concentrate light.

  • And so I started looking into this particular story a little bit more closely with the nice things about new buildings going up.

  • Of course, they have to have planning applications, and so you can actually go to the planning website, download all the plans for the building and take a look for yourself.

  • And so I downloaded the plans for this thing here.

  • So is one of the artist's impressions of what the building's going to look like, and the important point about it is that the south facing surface is curved to this building.

  • This particular architects like making these Kong cave surfaces, so it's actually it has the uninspiring official name of 20 Fenchurch Street course.

  • That's its address.

  • It's become widely known amongst Londoners as the walking, talking building, although they're announcing to be changing it to the rookie school building.

  • But just because it looks a little bit like an old fashioned working toe.

  • So the issue is that a concave surface is essentially, ah, way of concentrating light Akane Cave, especially.

  • I mean, I guess the important point is that if the if the sunlight that were hitting this surface all just went into the building, that will be fine, because the building would have no real effect.

  • But even with, you know, really good quality grat glass.

  • Some of the light gets reflected rather than going into through the windows.

  • And actually, as the light gets more and more oblique as the angle that the light hits, the glass gets more more oblique.

  • Typically, more and more of the light gets reflected, so if the light's coming in a fairly shallow angle to the glass, it's much more likely to get reflected.

  • If the lights face on, it tends to go straight through, and so as soon as you have light no face onto the glass.

  • You're gonna have a large amount of it reflected on because this surface is curved.

  • That's actually gonna then focus the light just as a conquering hero would.

  • So I had a little bit of a play around because I knew from the new story what time this guy had parked his car.

  • And so you can then look up in these things called ephemera is where the sun was in the sky.

  • At particular times I could figure out where the sun was.

  • It was pretty much a juice out.

  • So it was illuminating this particular surface pretty much face on, but also what angle it was at.

  • So you can figure out how high in the sky it was.

  • And then you could do this thing called a tracing of essentially figuring out where the different bits of sunlight will go.

  • Just using these simple laws of geometric optics of the light traveling in a straight line unless it hits the surface, and then the important law you have to use here is the lower reflection, which just basically says that the angle of incidence is equal to the angle of reflection.

  • In other words, if the act like comes into the particular angle.

  • It goes off at the same angle.

  • So I just downloaded this.

  • Started figuring out where the light when just doing it with a pencil on the protractor, one of these things for measuring angles.

  • And actually the hardest part.

  • This was finding a protractor because no one has won anymore.

  • But I did actually manage to borrow one.

  • Okay, so actually, I actually went round all the students saying, Can I borrow a protractor?

  • The general response I got was What's a protractor, which has been worrying but actually turned out.

  • One of them had this rather fancy looking protracted stuck on the end of a ruler in his desk.

  • So here's what's going on at that particular time of day.

  • So here's the sunlight coming in, and the sun's a long way away, which essentially means the rays of all parallel course, the razor, a sort of diverging from the sun in different directions.

  • But the sun sufficiently far away that to all intents and purposes, they're parallel here and you can see they strike different bits of the building, and then you can figure out the angle that they strike that particular bit of glass at, and hence where any reflected light's gonna go because he's angry and has to be equal to that angle out on because the building is curved, the angles get different at different points in the building.

  • And that's what causes this concentration effect that each one individually is just getting reflected back the same way.

  • It came pretty much sort of complimentary angle to the way it came.

  • But those angles are all different because the angle of the surface they're hitting is all different.

  • And so you can see the net effect is that all this will spread out sunlight coming in ends up concentrated in a rather small area.

  • And I did some very, very crude calculations to try and figure out how much it's concentrated by.

  • I reckon it's probably about a factor of 10 to 20 so that the intensity of light on that particular little bit of road was about 10 to 20 times what the usually intensity of sunlight is.

  • And it turns out for the plastic parts of cars enough to melt him.

  • This could be a useful property of code.

  • Oh, it's you know, it's in astronomy.

  • We use it all the time.

  • It's how you could focus the light in a telescope.

  • In fact, the reason why I got involved in doing these kind of calculations in the first place is because the people who wanted to figure out what these effects were gonna be thinking, Well, who is it?

  • Who knows what the properties of large reflecting concave surfaces are, And it's actually what astronomers duel the time we use this to actually collect large amounts of light and focused on down to small regions.

  • When you're looking at a distant galaxy, that's a good thing to do because you really want to collect as much light as you possibly can.

  • And even when you collected all that light is still very faint.

  • When you're talking about the son, you gotta be a lot more careful because there's a lot of like to start with.

  • So when you start concentrating it down, you really get huge amounts of power.

  • Tell us about your form here and not her hair.

  • So I am this The Judas privilege off.

  • Having created an urban myth here in Nottingham on the urban myth I created is in the middle of Nottingham, this thing called the Sky Mirror, which is a beautiful piece of art.

  • It's a conch aid mirror put there by an artist called Initial Kapoor, who makes these kind of installations quite a lot.

  • About six meters in diameter.

  • It's a large concave mirror and it basically reflects the sky.

  • So when you walk into this square outside the playhouse in the middle of Nottingham, you see this amazing mirror basically reflecting the skyline in the sky above you and you get these nice inverted image is one of the properties of a concave mirror is the images come out upside down?

  • Obviously, there are these health issues associated with large concave mirrors, potentially in direct sunlight.

  • S o.

  • I was called into this project to say Well, you know, one of the issues on I went through a lot.

  • You know what we've just been talking about?

  • About the dangers of collecting large amounts of sunlight and one of you even with them, this relatively modest mirror something six meters across.

  • You're still talking about many, many kilowatts of power, potentially being concentrated into a very small region.

  • So you really gotta be very careful about it.

  • It turns out in this particular case that they're being quite clever about citing it, so it's not a huge issue.

  • So unlike the skyscraper, where it's a south face that's really facing the sun, this mirror is designed to face North, which really means you very, really got get direct sunlight on it.

  • But there are a few weeks of the year in the middle of summer when the sun creeps around far enough that you do have to worry about it.

  • And so I warned them about all these issues, and they actually then decided that they were gonna put into mitigation, which was to put some sun shades up on the top of the theater a za way off, preventing the sunlight, getting onto the front face of the mirror.

  • Now to do that.

  • And they needed to put in a planning application.

  • And so they do be putting in the planning application one of the things that the people on the local newspaper here and not in and do as they go through all the planning application to see if there's any interesting they found this one for sunshades.

  • They've got in touch with the architect.

  • The architect settle will talk to this astronomy, tell you about it.

  • And it was a Friday afternoon and I was, you know, fairly laid back with my feet up on the desk, talking to this reporter on just in passing.

  • I said, You gotta be very careful about these things because if you weren't, then a passing pigeon could end up being barbecued as it flew through the beam.

  • And clearly it was a slow news day in Nottingham.

  • So this ended up being the banner headline on the front page of the newspaper about barbecue pigeons and the guys on the wire service, naturally, who go through a ll the local newspapers looking for entertaining stories.

  • And they picked up on this one.

  • And so they put it out on the wire service nationally and internationally and clearly it was a slow news day nationally and internationally, and I ended up being interviewed on the BBC and the story appeared in Australia newspapers, and it was all over the place.

  • And the poor playhouse, who actually paid for this wonderful piece of art to be put out, started getting all this abuse about where they were mistreating pigeons.

  • And so they ended up having to produce leaflets that said, You know, no pigeons were harmed in the production of this piece of art.

  • And actually, the chef in the Playhouse Causes Restaurant in the playhouse has clearly had a sense of humor because he put barbecue pigeon on the menu.

  • But even that what, 10 years after this, I still, once in a while people hear people talking about this mirror barbecuing pigeons.

  • I really have created my very own urban myth.

So there's been a new story going around the British media about a car melting in London, which apparently used you to its proximity to a new building, which is going up in London.

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如何融化汽車和燒烤鴿子----------60個符號 (How to Melt Cars and BBQ Pigeons - Sixty Symbols)

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    林宜悉 發佈於 2021 年 01 月 14 日
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