say there is a lake covered with 2 feet of ice. now, I was out ice-fishing on a lake with 2 feet of ice, and while waiting for a fish to strike, I couldn’t help but wonder; just how fast does a crack spread? I mean, I know unreasonably fast, but I was wondering just how fast… so, I’ll ask again, how fast would a crack spread through 2 feet of ice; and is there a universal speed for cracks to spread?
Thanks ahead of time
Ad Noctum, who likes to know all he can about a crack
Well, according to van Helfing’s theorem of advanced ice pressure in lakes smaller than 17.4 hectares under 65.38886 newtons at sea level with a temperature of -.02°C,
I dunno.
Given that the crack may result from pressures under the ice (temperature changes or flowing water) or pressures in the ice (as previously unfrozen sections expand to compress all the lake surface) or from any number of other sources, I doubt that there is a single number that you could come up with. Was there a pressure crack at that spot, previously, that is under new forces of expansion or torsion? Was that section of ice “undamaged” previously and is nowsubject to harder freezing or sudden thawing?
I suspect that there are way too many variables to calculate to come up with a “law” on an open lake. (There are probably some rules you could devise in a lab, but you’d never be able to transfer them to a “real life” situation.)
If your lake has frozen to a depth of two feet, you aren’t likely to have to worry about it unless you’re on Lake Erie or something larger.
isn’t that the truth–
I guess you’re right about all that was stated,
anyhow, Moderators feel free to close this thread at your conveniance, thank you
If this isn’t the most misleading title to a thread, I don’t know what is.
The thoughts I had as I waited for this thing to load up.
da/dN=A(delta-K[sub]I[/sub])[sup]n[/sup] in the region between delta-K[sub]th[/sub] and K[sub]c[/sub], although I’m not sure this is valid for ice. Hope that helps.
[sub]We could sure use Symbol font capability around here.[/sub]
this is verging on a WAG but…
I would think that a crack could spread at up to the speed of sound in the medium, so that would be ~3500 meters/sec.
-Luckie
Never more quickly than you can hand her the money.
The rate of crack propagation is not a constant for a given material. For a cracked material under constant load, the upper limit of crack speed is about 30 percent of the speed of longitudinal waves. So for ice, the maximum crack speed should be about 1100 m/s. The speed depends on length of the crack. It will start slowly and as the crack lengthens the speed will quickly approach this upper limit.
Most likely, if ice is cracking under your weight, the net load acting to open the crack will decrease rather than remain constant as the crack grows. This will slow or stop crack propagation, but the exact amount depends on the situation.