melting ice with object in it

[svandamme]

discussion at work

block of ice, 75 cm high
icesculpted Porsche Carrera, life size, on top of that block

in it, a set of keys for a Porsche Carrera



the car is outside, on a market square, it's not a cold winter over here, it doesnt' freeze at night at the moment, and we get day temps between 3 and 7 C ( in the shade)

guess the time in secs till the set of keys hits the ground, win the Porsche


that's the basis for the discussion
collegue, is a university bred type
i'm a high school dropout

so he says, easy, just take the weight of the keys, run some formula about the fixed sink rate of an object(mass) in ice, which is not variable and that's it


i'm guessing this sinkrate is A not as invariable, B there are more factors involved, C even if you did calculate it, that result would be of minor importance in the grand scheme of this melting thing

my guess is this sinkrate over the whole time span would be maybe a few inches or something, if it were a block off ice with no external factors, which is not the case, as there are many, many factors( external temp, water used for the ice, how old is the ice, how was the sculpture built, sun light, ice consistency, rain , etc et etc...)

je insists that the weight of the object, as a cause of melting under the object would be linear and predictable enough to come real close to the real result.. and snipped a few times "didn't you learn physics in school?!"

i'm saying, ok , you run the numbers, just make sure you let me have a test drive in it , once you win

any physics guru's who can shed some insight?

[sjf911]

I doubt that the pressure exerted by the keys completely embedded in the ice is capable of lowering the melting point to create a downward flow. It takes really high pressures to achieve. The effect is called regelation.

http://en.wikipedia.org/wiki/Regelation

[vash]

sorry, i am sucky with newton's law of cooling.

but that would chill one bigass glass of scotch!

[legion]

Why are you not out there with an acetylene torch?

[Rob Channell]

Just sneak out there one night with a propane torch....

Doh! legion beat me to it.

[ChrisBennet]

Torches are lame. Use frikken "laser".
-Chris

[Moses]

Sawzall. 5 Minutes. Do I win?

[pwd72s]

Better off buying a lotto ticket, the odds are better there.

[WI wide body]

Okay here's the formula:

Take the weight of the ice and divide it by the temp in F and divide that by the weight of the keys. Then multiply that number by 13.4217 and you have the number of minutes. The exact number of seconds is dependent on global warming in that particular area.

This secret and highly classified formula was extrapolated from a friend under a bridge who did happen to sneak into a Motel 6 one night so it should work.

Good luck and save me a ride.

[masraum]

I agree, the keys won't "flow" through the ice.

If it's sunny, and the ice is clear enough for the sun to hit the keys, then the sun will warm the keys which may cause them to melt through the ice faster.

[svandamme]

guys, the block of ice is guared
they've done this before, last year it was a gold bar


tx steve for that regelation link, from that formula , i can imagine it's going to be pretty tough calculation...

0.0072 °C drop of melting point per additional atm of pressure applied?

i mean, "how much nm of force do keys exert?"
somebody get me a super computer, we need accuracy here this is a mission of great importance!!

[Noah930]

Regardless of whatever analyses, computations, and Cray supercomputers you use to try to figure out the answer to win the prize, in the end--just like when picking for the NCAA March Madness basketball tournament--the chick who reluctantly agrees to join the pool just to get everyone to stop badgering her, and picks teams based upon the names of the mascots or colors of the uniforms, will win it all. She won't even be the least interested in cars, by the way.

[M.D. Holloway]

You could make a smaller more manageable size replica out of ice and do a simulation and figuer it out.

The dimensions might be tricky though. One thing you could do is make a mold of a smaller version of that car - use a MiniChamps model as your positive for your smaller version and time its melt in the same condisitons then just extrapolate for the larger scale.

That is a pretty big block of ice so the weight of the keys might be pretty in significant untill its a few cm from the ground. A simple experiment could provide data for this as well. In fact, if you had a few different blocks of ice cut to varying thicknesses with keys frozen inside you could time their melt rate and come up with the an equation to predict the thaw. The trick though is the fact the your temp fluctuates so unless the temp is constant it does make predictions tricky. You will never know precisely how warm/cold it will be on a given day or night.

Noah may have the best suggestion. Find the hot babe with no brain and ask her for the number or her number...

[svandamme]

Wayne, that's what i told him , impossible to calculate with a simple linear formula, he kept saying no, no no, it all doesn't matter, it's just the sink rate
doesn't matter if you take a block of ice 10x10x10 feet, or a narrow cyllinder, 1 feet across , 10 feet high...

that's what pissed me off, i know i'm not a uni grad, but i'm not to stupid to use my imagination, and imagine what factors might affect this whole ordeal,

and once i came up with a number of variables, it seemed pretty clear to me that you just can't calculate this, let alone calculate it with a simple formula.

this regelation thing might even be true, i'm not debating that, i just think it's effect is marginal to say the least, compared to all the other factors

0.0072 C degree decrease in melting point for every ATM increase in pressure?

PAA-LEEEASE what are we talking about here when the subject applying pressure weighs something like, i dunno, 150 grams??

(if anybody has a 997 key with him, and a small scale at hand, for ****'s&giggles)


i agree Noah, it's a guestimation lottery
even if the formula was reasonably accurate to use, it'de still boil down to luck, maybe it would narrow the playing field a bit

but as it stands, there's not enough data, and not enough computing power to actually narrow it with enough accuracy to rely on...


Lube, the dude insists that external temp has no influence on this sink rate inside, argument is , that the external temp never get's to go that deep in the ice, as the ice absorbs it on the outside, now i can agree to some extent with that... but as ice is translucent, the solar energy does penetrate... and that's another one of those things that's near impossible to calculate

then there is ice quality
what water was used? de-mineralized water?
how old was that ice? i know that in sweden they have an ice hotel, they cut the ice blocks in spring, to use em next winter, so the ice settles... is that a factor in this setup? who knows?

this small scale thing is probably the most realistic to calculate the melting of the whole block
but regarding the keys, the smaller scale you go, the more inaccurate you can measure/extrapolate the key behaviour, so that's no good either
and it still doesn't cover the variables of a block of ice on a market place, exposed to the elements...

[sketchers356]

As a physicist your friend is an idiot. I agree with most all of your points to it being a terrible pain in the A$$ to calculate.

[M.D. Holloway]

External temp has everything to do with it! The sink rate is meaningless until the keys are a few cms from the ground, until them the ice will provide adequate support.

As for external temps - your friend should live in a Florida orange grove in the winter. They will spray the fruit with water if there is a frost coming and projected temps get below freezing. Why? becuase ice doensn't get colder than 0C and the fruit will tolerate 0C but not lower - the thinn film of ice will actually insulate the fruit from getting any colder.

As kids, we could make igloos and it would actually get rather warm inside them when the outside temps were -10C or -15C.

Those keys are going to sink in porporation to the shinking of the ice which is absolutley dependent on the ambiant temp.

[M.D. Holloway]

Agree, the small scale will be difficult for key drop determination - that is used more for a rate determination for the shape. A block could most likely be substituted that is in the same general shape I suppose. What would be the tough thing is the ambiant temp fluctuation. Water quality and even the way in which the water was frozen to make the ice. I know that freeze rate and storage temp do play an influance on the ice clearity which would suggest that the formation of the ice chrystals are in fact different at different process conditions. Of course if this was a material like glass, matel some plastics it would have have an influence on the behaviour of the material - water is really a strange substance. Not many things actually expend when they freeze, water will do that.

You got me thinking now. I know that there is enough data on the kinetics of water to model this but the thing that does make it so friggin random is the ambiant temp flucuation and also the fact thatthey want it in seconds! You would have to know the exact temp of the freezer where the block was kept, if it was sculpted in the freezer, what the temps were on route to the park and then what the temps were going to be in order to calculate the thaw rate.

Its doable but there are a bunch of dependent variables that have to understood prior. I would think that a physical chemistry class has done this sort of work. If not, it would be an interesting class exercise on thermodynamics.

Cool...

[Mo_Gearhead]

Another factor is how much sun is going to hit the object. Reflected off the ground/pavement it sits on. It will melt faster at the base and if the sun gets
to beam down on those keys/key fob (darker than the ice?) that will hasten their drop near the end game.

IE: Build a snow man, use 'coal' for eyes/buttons/nose, add sunshine - observe.

[vash]

no way, i think the biggest unknown is the amount of air moving past that block of ice. more air movement=faster melt.

[svandamme]

thx guys, i knew i could count on the brain trust

i'll make a nice summary of it, and have him chew on it