Since ice floats, why, when I put crushed ice in my mug and then add the liquid, does it take up to a minute for the ice to rise to the surface? And why have all of the separate pieces of ice “melted together” into one solid lump?
The more things change, the more they stay insane.
Liquid H2O is highly cohesive. The finely forming layer of liquid H2O on the surfaces of the ice will “lump” the ice together.
The liquid is also quite cohesive to glass. The ice is often prevented from floating until it can overcome the cohesive forces.
Also, there are frictional forces to overcome along the walls of the glass and/or between ice bits - depending on the size of the ice cubes or ice “lump”. (No, ice is not a frictionless surface.) So some bits of ice can be blocked by others
Bottoms up!
I’d rather have a bottle in front of me than a frontal lobotomy - Hawkeye 4077th
Jinx, that all makes sense, but why do the pieces of crushed ice actually freeze together? We’re talking a solid mass here–and as time passes, the outlines of the individual pieces of crushed ice disappear and it becomes one solid (albeit smaller) lump.
I’ve noticed that this behavior seems to be exhibited more when the liquid is at refrigerator temperature before being poured over the ice.
The more things change, the more they stay insane.
Redbeard, the water/ice interface is right at 32 degrees F. Since the ice is crushed, there is a lot of ice surface, and the water at this surface is at the freezing point. So this water will tend to freeze.
It may help to think of the crushed ice as a porous solid piece of ice (it isn’t exactly, but this may help you visualize). When you pour liquid water onto it, some of the water flows into the “pores” and freezes there. This has the effect of freezing the individual pieces of crushed ice together.
Redbeard–couple of other things to keep in mind.
Ice floats in water, but just barely. Some of the delay is because of the ice’s low buoyancy.
Something floats when it displaces its weight in water. In order for the ice to float, you have to pour in the equivalent amount of weight in water. That’s the weight of the entire mass of ice.
If you’re pouring in a foamy beverage (e.g., diet Coke), you’ll see three layers–liquid, ice, then foam. The foam is light, but not weightless. It’s weight will push the ice down into the liquid.
In keeping with CatInHat, the ice-water mix is at 32 F. The interface, per CatInHat, is in equilibrium and the liquid between adjoining bits of crushed ice can readily reform into ice.
I’d rather have a bottle in front of me than a frontal lobotomy - Hawkeye 4077th
Guy Propski writes:
While the first statement above is true, the conclusion is not. Note that the volume displaced is measured relative to the final surface position of the fluid. In a small container, the surface height is greatly affected by the added material. So, the displaced liquid does not necessarily have to be there in the first place, if that makes any sense.
Rick
I’m not sure I follow you, Rick. Can you expand on that?
I love this technical jargon. Usually when the ice takes a while to rise for me, it is because of what CatnJinx said, interface and cohesion and equilibrium. A small amount of liquid in the bottom of the glass,the large amt of ice freezes that that little bit of ice sticks to the glass the large amt sticks to the small amt untill the larger amt of beverage melts that interface.The crushed ice will stick to itself in air.The surface melts but the mass of all the ice freezes that thin skin of water together.That IS what you guys said isn’t it? Rick,if I understand what you are saying, I think you are wrong. To be bouyant something has to displace more than its mass in an equivelant volume.I don’t think it has anything to do with the surface level or the size of the container.There has to be enough volume and mass of liquid to be displaced or it wont float. But I could be wrong, I have had water on the brain for a while now and my thinking process is frozen…
“Pardon me while I have a strange interlude.”-Marx
OK, let’s see if I can explain this better:
You are correct that the volume of water displaced by a floating object has exactly the same mass as the object. The question is , how do you measure the displacement? The answer is that it is the volume of the displacing object (ice, in this case), that is below the water surface. It has nothing to do with how much fluid surrounds the floating object (as long as the final depth is enough so that the object doesn’t scrape the bottom of the container).
Try this gedankenexperiment:
Consider a cylindrical container of water with a cylindrical cork floating in it. There is some distance between the bottom of the cork and the bottom of the cylinder (which is the definition of floating, of course). So, we can obviously still float the cork in a cylinder with the same diameter, but with a depth that is much reduced, so that, for instance, the bottom of the cork is only 1 millimeter from the bottom of the container.
Now the sides of the cork are, in general, some distance from the walls of the cylinder. So let’s use a cylinder that is much smaller; specifically, with a radius 1 mm larger than that of the cork. We can leave the depth the same as it was before, with the bottom of the cork being 1 mm from the bottom of the container.
Do you agree that the cork is still floating (neglecting surface tension effects that might cause it to stick to the side of the container)? Good. Now, we have made no absolute reference to the size of the cork, only to the size of the container relative to the cork. If the cork is sufficiently big, the amount of water can be made quite small relative to the weight of the cork, but it will still float.
Does this make any more sense?
Rick
Regarding the ice fusing together, aren’t ice cubes taken out of the freezer chilled to well below 0 celsius? They would tend to freeze some additional liquid onto them before warming up enough to start melting again.
I can’t believe Cecil hasn’t stepped in yet to set you folks straight. It is neither necessary nor relevant to invoke concepts such as cohesion, displacement, equilibrium, or interface. You might as well blame hydrogen bonding or Van der Waals interactions.
<img src=“http://rainbow.ldgo.columbia.edu/ees/climate/slides/density.gif” align=“right” border=“0”>
Water is an exceptional substance which experiences a decrease in density when it undergoes phase change (i.e., freezes). However, water behaves as a conventional liquid when heated (i.e., the warmer it is, the lower its specific gravity).
Ice takes its sweet time floating to the top of your beverage because it is more dense than your room-temperature beverage. It is only after your beverage drops below 10 [sup]o[/sup]C that the ice is of a lower density than the beverage.
As for the reason ice clumps together, it is a matter of dynamic equilibrium–although the general trend for an iced beverage in a room-temperature environment is ice–>water, the molecules of liquid H[SUB]2[/SUB]O and solid H[SUB]2[/SUB]O exchange energy, resulting in an exchange of phase: think of it as two steps forward and one step back and you’re getting the idea.
I can’t believe Cecil hasn’t stepped in yet to set you folks straight. It is neither necessary nor relevant to invoke concepts such as cohesion, displacement, equilibrium, or interface. You might as well blame hydrogen bonding or Van der Waals interactions.
<img src=“http://rainbow.ldgo.columbia.edu/ees/climate/slides/density.gif” align=“right” border=“0”>
Water is an exceptional substance which experiences a decrease in density when it undergoes phase change (i.e., freezes). However, water behaves as a conventional liquid when heated (i.e., the warmer it is, the lower its specific gravity).
Ice takes its sweet time floating to the top of your beverage because it is more dense than your room-temperature beverage. It is only after your beverage drops below 10 [sup]o[/sup]C that the ice is of a lower density than the beverage.
As for the reason ice clumps together, it is a matter of dynamic equilibrium–although the general trend for an iced beverage in a room-temperature environment is ice–>water, the molecules of liquid H[SUB]2[/SUB]O and solid H[SUB]2[/SUB]O exchange energy, resulting in an exchange of phase: think of it as two steps forward and one step back and you’re getting the idea.P
Hmph, worked when I tested it.
Oh sure, PatronAnejo, we all just carry around these handy-dandy little charts. Of course, we should all have known that cohesion plays no role at all nor equilib nor hydrogen bonds nor London forces nor Brownian motion. Goodness me, but what were we ALL thinking??? :rolleyes:
The answer is so bleeding obvious, isn’t it?
I’m glad we paid someone the big bucks to discover a 10 C threshold. 
By the way, Patron, not to burst your bubble or anything, but we had the clumping issue licked. 
Sprite tastes better - they’ve proved it!
Wiley Coyote: Supergenius!
I’m surprised no one else has brought this up. When you put the crushed ice in the glass, it’s colder than 32 degrees F. The first water that comes in contact freezes because it gives up heat to the ice, without even melting the ice, solidifying the entire mass. Also, that little bit of water freezing will expand, temporarily wedging the mass into the sides of the glass.
Only after the water and ice come into equilibrium is the ice-water mixture at 32 degrees.
Regarding buoyancy, as long as the object (ice in this case) sits on the bottom, it displaces only the volume. Once the displaced mass equals the mass of the object, the object is neutrally buoyant, and more liquid will then float the object. At that point, it is displacing the volume of liquid that has equivalent mass. Thus the ice floats with a 70/30 split; that is the ratio of the densities.
Regarding the cork experiment, the cork will float as long as it displaces it’s mass worth of water. Once the mass of cork is greater than the displaced mass of water, the cork hits bottom and only displaces it’s volume (or the submerged volume, if it’s too tall).
PatronAnejo, I don’t accept your explanation about the 10 deg C temp difference in densities being the reason. Specifically, I don’t think the density difference in ice between those temps is very significant - from your chart I estimate about 8 ten-thousandths of a gm/cm3 (Is there a code for super/subscripts?). How much does the density change in the liquid by cooling? Assuming the liquid is water (for simplicity), what are the density values?
In particular, see the difference between floating crushed ice vs. cubed ice. If you pour the water in, it will float once the right volume is added, time/temp irrelevant. I think the crushed ice takes longer for the reasons others stated. It is adhering to the sides. Think of it this way - if you freeze a clump of ice in the bottom of the cup, then pour liquid on it, the ice will stay at the bottom, even if there is enough water to float it, because it is adhering to the glass, and water cannot get below it.
Also, have you ever done the experiment with a carboard tube, sugar (or other granulated substance), tissue paper, and a stick? You put a layer of tissue paper over the end of the tube, and declare you can jam the stick as hard as you can and not break it. How? You fill the tube with the granulated substance. Then when you press with the stick, the pressure is transferred into friction between the grains, and push equally outward against the sides of the tube as downward. Thus the strength of the tube pretects the tissue paper. It is the same with the crushed ice, which is granulated, and the water pushing down on it, pushing it against the walls. Add the thermal factor of the first liquid in contact freezing and sticking it all together and against the walls, and you have the friction that must be overcome. As the temperature settles, the new ice grips melt again, and the clump of crushed ice then floats.
Finally, for the best cooling with least diluting of your beverage, use one large chunck of ice, not small cubes or crushed ice. Less surface area. More thermal mass.
Hmph? I still find that friction still plays a role in determining how quickly the ice will float. Friction, for example, is between ice and walls of my glass- especially fancier glasses with walls that are not smooth. One “bang” of the glass on the counter, and up floats the ice. So, friction can hold back the ice cubes/clump even if the ice is at your threshold temp. Hmph!
