andy (04/06/83)
If one puts an ice cube in water and then one measures the level of the water. Does the level of the water increase, decrease or remain the same after the ice cube has melted? Explain FULLY. This question was on an NSF scholarship exam many years ago. Can anybody answer it? -- Andy Rodnite Periphonics Corp. floyd!peri!andy
pn (04/07/83)
I believe an old fart named Archimedes answered that question many years ago: a floating object will displace a volume of water weighing the same as the object. therefore, no change in water level when the ice melts. (because the weight of water is the same as the weight of water)
mclean@NRL-CSS (04/07/83)
From: John McLean <mclean@NRL-CSS> Expanding on Phil Ngai's answer, the ice floats since water is one of the few substances that expands when it freezes. This is due to hydrogen bonding and is what makes it possible to ice skate. john
vax1:swifty (04/07/83)
A couple of years ago I had an argument about this with another engineer (who happened to be a physics graduate). Not willing to accept the answer he spent hours (days?) calculating densities, weights and just about everything he could to try to prove that the level is not the same. I think he finally concluded that it wouldn't be the same because of trapped air in the ice. However, for perfect ice and perfect water the level will be the same. swifty
pn (04/08/83)
Also note that if ice sank, most of the oceans and many lakes would end up mostly frozen. The top few feet may warm up during the day, but since warm water rises, very little heat would make it to the bottom. Frogs and fishes would have a hard time.
palmer (04/08/83)
Air in the ice would make no difference at all, if it were at atmospheric pressure. There would be a very, very slight increase in the water level when the ice melted, due to the fact that the ice cube is also displacing air. (Imagine that the ice expands a lot, so that it ends up at the density of helium. The ice would float in air, but when it melted it would increase the water level, even though it displaced no water when it was frozen. Scale this down a bit, and you have the effect.) Of course, if you take into account this effect, you might as well go all the way and worry about the Earth's gravity gradient. This would also decrease the weight of the ice, so the water level would rise when it melted. David Palmer
MERMAN%MIT-OZ@MIT-MC (04/08/83)
From: Dave Goodine <MERMAN%MIT-OZ@MIT-MC> It depends on the amount of air trapped in the ice-cube, assuming that we're talking about the about a common ice cube, known to have air bubbles occupying about 10 to 15% of the space the cube displaces in a container of water. (The air is obviously why ice floats in water.) If the cube contains no air(which i'm not sure is even possible), then it will fall to the bottom and the level of the water will not change as the cube melts. But, when the the cube has air of mass A trapped inside, it floats with M mass(M being the value of some function of the absolute amounts of air and water in the cube) above the water. I don't know exactly what the function would be, but logically, we can say that, since all of the air in the ice will be released from the system, then any change in the level of the water will be (M-A). Dave Goodine <MERMAN@MIT-OZ>
pn (04/10/83)
"The air is obviously why ice floats in water" Please don't shame my alma mater by saying things like that in public. I suppose you believe that if you get a long run of heads when flipping a coin you're more likely to get a tail next time?
emma (04/10/83)
The air is obviously the reason ice floats in water -- WHAT?!?!? Ice floats in water because water expands when it freezes. -Joe P.
debray (04/11/83)
"The air is obviously the reason ice floats in water" : HUH? Ice floats in water because water is one of the few substances that expands when it freezes. (Actually there are several different kinds of ice, as a complete phase diagram of water will show ; they are formed under different conditions of temperature and pressure, and to the best of my knowledge, all have specific gravities less than 1.0). The only other substances that I can think of that expand on freezing are bismuth and bronze (that would explain its popularity with statue-makers of yore : on expansion, it would take up the impression of the mold really well). Saumya K Debray SUNY at Stony Brook ... allegra!sbcs!debray
mcewan (04/11/83)
#R:peri:-20100:uiucdcs:24400030:000:109 uiucdcs!mcewan Apr 10 17:37:00 1983 Actually, I would expect the water level to go down, from evaporation as you're waiting for the ice to melt.
soreff (04/12/83)
I think that there are several other substances which expand when they freeze besides water and bismuth (I'm not sure about bronze). I'm fairly sure that germanium is in that class, and possibly some silicates. -Jeffrey Soreff (hplabs!hplabsb!soreff)
lwall (04/18/83)
Reply-To: lwall@sdcrdcf.uucp (Larry Wall) Organization: System Development Corporation--a Burroughs Company References: <uiucdcs.1855> ********* "Actually, I would expect the water level to go down, from evaporation as you're waiting for the ice to melt." ********* Actually, at normal humidities, I would expect the water level to go up, from condensation as you're waiting for the ice to melt. Or does all the condensation have to occur on the outside of the glass? Klein bottles, anyone?