Comments on: Paneful Jigsaw

By: Clifford

Clifford — Tue, 04 Sep 2007 21:36:01 +0000

I’m not an expert, and I’m sure that there are studies of this, but I would guess that this is really the most natural solution, since stress is very local, and communicated by local processes, so disconnected responses like concentric circles would seem to be ruled out on that basis alone. That leaves lines coming out of the impact point, and the question of why they are radial and, say, spiralling. I’d have guessed radial since that is the shortest path outward from the source, and secondly, because its the only thing consistent with the symmetry - what would determine the curve direction of the spiral? So in an infinite sheet of glass with no preferred history of defects pointing one way or another, I’d say there’d be a radial pattern because of locality and symmetry.

Maybe a true expert will stumble upon this post and say more - or point out that I missed a major issue - so check back from time to time.

Cheers,

-cvj

By: Des

Des — Tue, 04 Sep 2007 21:19:52 +0000

Hi Clifford:

Thanks for a fascinating post. I was wondering why radial lines more efficiently relieve the stress (in an infinite pane of glass with no edge effects) rather than another configuration, eg concentric circles? Pehaps it is somehow related to the amount of area encased by the break (energetically desirable) relative to the length of the break (energetically undesirable)?

Cheers,

Des

By: Amara

Amara — Tue, 04 Sep 2007 10:40:39 +0000

Glass-

I have a car that my colleague gave to me instead of putting in the junk yard. At times I’ve hung onto the driver’s door while driving because the broken door latch didn’t catch, the battery continues to need to be replaced because there is a leak in the electrical system somewhere, the driver’s side electrical window doesn’t work, and the seats don’t adjust any more. However I’m proud that I’ve managed to keep the car’s engine in good mechanical shape, while the car’s body disintegrates or falls off.

A couple of years ago, my interior mirror fell off, so I ran to the hardware store and bought some superglue to glue it back on. I didn’t read the package very well though, because it said clearly *Not For Use on Glass*. Yes indeed, the next day after gluing my mirror to the inside of my front windshield, some lovely new cracks formed around the point of contact of the mirror and one of those cracks reached a tentacle downwards. I asked some glass people how much time I have, and they expected that it would reach the bottom of the windshield within a few months. “But anyway, don’t worry,” they said, “automobile glass is two layers with the outer layer not affected by the inner layer, so I’ll still be protected when it rains.”

Well, I keep watching that downward crack, and last summer it seems to have stalled in the midpoint of my front windshield. It has been a fascinating study in glass mechanics.

By: Clifford

Clifford — Tue, 04 Sep 2007 06:02:40 +0000

Hi Amara,

They are not in pots. Interesting tip. I think they’d be fried by the sun if I did do that. The new screens are doing the trick, though.

Hi Elliot,

The hand is fine. Fully healed. It was just a small nick.

Best,

-cvj

By: Amara

Amara — Tue, 04 Sep 2007 05:33:35 +0000

Dear Clifford: A trick on the flies that some German family friends told me: If you put tomato plants near the window openings, it deters flies. I haven’t tried it myself, so I don’t know if it is a wives tale, but if you have any of your tomato plants in pots, it might be worth a try.

By: Amara

Amara — Tue, 04 Sep 2007 05:25:14 +0000

I’m ok with most bugs, however, fleas, mosquitoes and cockroaches are the ones that bother me. I’ve accidently broken light fixures trying to kill mosquitoes, and by cockroaches, I mean the ones that are about 5 cm and fly (I’m squeamish on those).

I have a business arrangement with the daddy long leg spiders that I will let 5 cohabitat my apartment (the others I catch and put outside), because they catch the other bugs.

By: Elliot

Elliot — Tue, 04 Sep 2007 04:42:52 +0000

I hate flies too. I usually stop whatever i am doing and kill them. They are very unclean creatures. I’d rather have a thousand cockroaches, than one fly. But I suspect others feel differently. Sorry about your hand.

Elliot

By: Carl Brannen

Carl Brannen — Tue, 04 Sep 2007 00:31:36 +0000

Cracks tend to occur where stresses were concentrated before cracking, but the cracks themselves are a form of stress relief. That is, when the glass cracks here, stresses are relieved near that area, so the next crack is relatively far away.

A microscopic crack in a crystal is called a dislocation. Interestingly, these tend to have properties that remind one of the Lorentz equation.