h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I found a caterpillar in an artichoke once but I still eat them because they are one of my favorite foods. I just check each piece really carefully before I put it in my mouth

Hello,

To be pedantic, the US Food and Drug Administration has all sorts of regulations that specify such things as the maximum allowable insect legs allowed in a chocolate, fruit fly eggs in fruit, etc. I don't know if this reflects the actual distribution of legs in a bar. In general, I think the insect legs come from the agricultural processes used to collect ingredients for the bar (cacao beans, peanuts, dairy, etc.) and not from the factory.

And hey, it's extra protein.

Yours,
Jake

How do they count them?
Counting legs sounds like an incredibly boring job.

How would you find the legs? I mean, they're pretty small, do they have to go look through all the chocolate that goes into chocolate bars and make sure they have the right amount of insect legs?

I truly feel really bad for anyone who has that job.

All accidents in Britain occur within 75 miles of the sea. But there is a very good reason for that.

Is that because all of Britain is within 75 miles of the sea?

If you went up a very high mountain and had an accident on the summit, would that count as being further from the sea?
Also- is it true that glass is a supercool liquid?

Yes, surely if you are up a mountain you would have to be a greater distance from the sea then if you were at sea level. I don't know if it counts, but it's difficult to deny. It wouldn't even have to be a high mountain. Down a mine should do, as well.

I was taught at school that glass is a supercooled liquid. I was assured by my chemistry teacher that if you were to make a pane of glass of constant thickness, waited a few years and then measured it, that it would be thicker at the bottom. I think it would have to be quite a few years, and the measuring equipment would have to be very sensitive, but there is some pretty old glass around, and very sensitive measuring thingies (excuse technical language). Somebody must have had a go.

Yes, there's lots of old glass around in Central Europe. Some the old churches and monasteries have some of their original windows, and the glass is always thicker at the bottom.

You don't need fancy equipment: go to a church with stained glass thats a few hundred years old and you'll see that the glass is much thicker near the bottom of the pane.

hee hee, simulpost

Does anyone know how long it would take for glass to do that?
Just wondering...

It doesn't take too terribly long. In 1996 I lived in a house that had been built in 1921 or thereabouts. I could see even then that the glass in the windows (the ones that had their original glass, anyways) had been flowing all that time, so that the panes were thicker at the bottom as if they had been poured into place.

In astronomy, this is not a useless fact at all. Telescopes that are made with lenses (refractors) can't be as big as telescopes made with mirrors (reflectors) for this very reason. The primary lens of a refracting telescope is supported by its edges up in the front end of the tube. If the lens is larger than roughly a metre across, it will deform under its own weight and will no longer be the right shape to focus light properly. On the other hand, a reflector's primary mirror lies flat against the back end of the tube, with its entire surface supported. I seem to recall that the largest single telescope mirror in the world has a diameter of 8 metres. If you want a larger mirror, you have to make it out of lots of little mirrors.

*goes to check the old windows in her house built in the 1920's*
Hey! Cool! It is thicker at the bottom!

I've just looked for information on this subjects and the results aren't what I expected...

It seems that the only vaguely reputable study undertaken on this subject is a paper entitled "Do cathedral glasses flow?". I've only found a summary, but the answer would appear to be no. The author argues that the appearance of flow is merely due to the way the glass was manufactured, and that it would take longer than the life of the universe for such an effect to be visible. Without getting bogged down in all the technical stuff (because I've not got any to work with), why should stained glass which is only a few centuries flow, when glass vases that are several millenia old don't?

With regard to the lenses mentioned above, that's not the same issue: metals also deform under their own weight and they're not liquids.

As a side issue, I've had a look at a glass viscosity/temperature chart and while it doesn't show anything below about 200°C it looks very much like glass is going to close to infinitely viscous at room temperature. Whether it is or not, isn't it possible that once you attain a certain level of viscosity, even if the glass could theoretically flow, gravity won't be enough to overcome the inertia?

You may be right about the lens thing, actually... lots of materials do that, but some are viscous and some are not. I think a metre-wide slab of glass standing on its edge would probably deform in a different pattern than a similarly-shaped and -sized piece of metal.

How do we know that the millenia-old vases don't flow? We don't know exactly what shape they were when they were made, or how thick the glass in various places originally was. With a pane of glass, you go on the assumption that the pane had a more-or-less uniform thickness when it was made. In a window, you would probably see the widening at the top of the pane as well, but it would be because the top edge of glass is attached to something. It would be thick at the top, then there would be a thin patch, and then it would get progressively thicker.

Good point.
Hmmmm.....interesting....

Old physics lessons are coming back to me and I seem to remember that glass does apparently flow. Glass-vases do not 'flow' due to their shape. If you think about it a pane of glass is simply a sheet - the molecules can move slowly under the influence of gravity - nothing to stop them, but if you look at a vase it has a bottom - so the molecules cannot flow downwards - they have nowhere to go...that's the only explanation I can think of at the moment, it probably has a fatal flaw - but I think it makes sense.

Pedantic man to the rescue!

According to the smart folks at Corning:
"Glass does not flow to a measurable extent at room temperature even over very long periods of time. Thickness at the bottom, the sides and the top of the segments that make an entire Medieval stained glass window happened by chance in the cutting, and as a result of the manufacture of the disk from which they were cut."

Apparently, glass could flow, but it would take a really long time (over >10M years) and result more in a shortening on the shape, rather than a thinning at the top with a thickening in the bottom.

Yours,
Jake