Why does ice make crackling sound when you pour liquid over it?

Discussion in 'General Science & Technology' started by wegs, Aug 10, 2020.

  1. wegs Matter & Pixie Dust Valued Senior Member

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    https://www.mentalfloss.com/article...-crackling-sound-when-you-pour-liquid-over-it

    I've often wondered what causes the sound of ice ''crackling'' in a glass, when water is poured over it. So, ''differential expansion'' is the answer, but I'm wondering if we let ice sit out at room temperature for say ten minutes, would it crackle, as if it came straight from the freezer?

    Fascinating that glaciers go through a similar process when melting, but on a far greater scale. But, from what I've been reading, it sounds more like bubbles popping, than ice crackling.
     
    Last edited: Aug 10, 2020
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  3. DaveC426913 Valued Senior Member

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    It may still crackle, yes.

    I've had ice crack in my glass ten minutes after I poured pop in.
     
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  5. wegs Matter & Pixie Dust Valued Senior Member

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    Cool! Now that I know why, I can't wait to have people over for bbq's and such, and share my newfound knowledge as the ice crackling commences.

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  7. arfa brane call me arf Valued Senior Member

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    It's called cavitation.

    oops no that's in liquids. I think it's a similar process though because of sudden pressure changes.
    And I'm pretty sure it happens when ice is exposed to warmer air, like when you take ice out of a freezer.
     
    Last edited: Aug 11, 2020
  8. Seattle Valued Senior Member

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    I'm sorry but you can't have people over...Covid.

    In racist America you must have a house that is in an unsafe neighborhood and therefore it would also be unsafe to have people over for that reason as well.

    Sorry. As the woman of the house you need to be more careful.
     
    Last edited: Aug 11, 2020
  9. arfa brane call me arf Valued Senior Member

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    Wow. Somehow that seems so deep and meaningless.
     
  10. wegs Matter & Pixie Dust Valued Senior Member

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    I’m not sure what to reply, here lol
    Science is never meaningless.
     
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  11. exchemist Valued Senior Member

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    It's just cracking due to thermal expansion at the surface of the cube, while the centre is still cold, leading to a sudden failure of the solid structure, like what happens with glass if you cool it too rapidly from hot. The sudden movement of part of the cube, when it gives way and the tension is released, creates a sound wave, in the liquid and then in the air.

    Cavitation is due to shock waves caused by the sudden collapse to nothing of low pressures voids in a liquid, containing only liquid vapour. Typically these are caused by a very sudden displacement of a solid surface, occurring too fast for the liquid to flow into the space vacated. Classic examples are motor boat propellors, or pump rotors, spinning too fast and losing their "grip" on the liquid they are immersed in. Another example can be vibrations in the block of an IC engine, leading to cavitation erosion of the cooling system.

    I suppose it is conceivable that the sudden movement in a fracturing ice cube could be fast enough to cause some cavitation, but I have never seen this described.
     
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  12. paddoboy Valued Senior Member

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    Or to put it more simply, caused by the action of the state of matter of water ice, changing to the liquid phase, suddenly and unevenly.
     
  13. arfa brane call me arf Valued Senior Member

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    Does the cracking or crackling sound happen in frozen liquids other than water? How much is it related to the way water expands when it's cooled from 4 to 0 deg Celsius?
     
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  14. DaveC426913 Valued Senior Member

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    A very good question.
    I think a lot of it is due to water's penchant for not following the rules.

    Are there any other liquids whose solid phase floats in its liquid phase?

    Can't find another liquid with this anomaly.

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    For example, mercury just gets more and more dense as you cool it.

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    Last edited: Aug 12, 2020
  15. exchemist Valued Senior Member

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    I'm not convinced the expansion of water on freezing is relevant to this.

    Nor do I think the presence of a liquid is relevant.

    A tray of ice cubes taken from the freezer will often start crackling before any of the cubes are put into water. I think it is merely that water heats the surface of the cube faster than air and thereby introduces more severe expansion stresses in the ice, so you get more cracking noises after putting it into water.

    The process is due to the normal expansion of ice as it is heated from -20C to 0C. The unusual reduction in volume when ice melts won't be relevant. I am sure other brittle materials exhibit the same behaviour - I've already mentioned glass, for instance and some rock weathering processes are due to the same basic phenomenon, though occurring more slowly.

    But the introduction of the expansion of ice on freezing into the discussion reminds me of one factor that may be relevant - hydrogen bonding. It is hydrogen bonding that is responsible for the open structure of ice. Ice is quite mechanically weak, because it is held together only by these hydrogen bonds, which have only the strength of around 10% of a normal covalent bond.

    P.S. There are one or two other materials that expand on solidifying from the liquid state. Bismuth is one.
     
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  16. arfa brane call me arf Valued Senior Member

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    When you take a tray of ice cubes out of a freezer it's nominally at 4° so the crackling sound is some function in this linear region, up to the melting point of ice. (see the first of DaveC's graphs above)

    It must be a function of what happens to hydrogen bonds as they 'warm'; a kind of annealing. The crackles must be an effect of the still-solid state of all the bonds involved in the generation of sound (?). In cavitation the bubbles coalesce into larger bubbles, I'm pretty sure cavitation and sound go together.
     
  17. wegs Matter & Pixie Dust Valued Senior Member

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    Would adding salt to the water within an ice cube tray prevent the cubes from ''crackling'' when pouring a beverage over them? (since salt lowers the temp of water)
     
  18. exchemist Valued Senior Member

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    Interesting.

    As I have been saying, the cracking is just the result of the surface of the ice getting suddenly warmer and expanding, while the interior remains cold, setting up stresses that crack it. The same would in principle happen if there were salt in the water of the ice cube, the only difference being that the cube would melt at a lower temperature, due to the freezing point depression caused by the salt. (Salt does not lower the temperature of water, it lowers the freezing point of ice.)

    However, if that meant that the surface of the ice cube immediately melted, instead of expanding as a solid, there would be no expansion stress created, and no cracking. So yes,

    But your drink would taste terrible, of course.....

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  19. DaveC426913 Valued Senior Member

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    Not sure I follow. No freezer is set at 4°.
     
  20. wegs Matter & Pixie Dust Valued Senior Member

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    Right, sorry - that’s what I meant - so it means that the water won’t freeze as easily, if salt is added? But it will freeze nonetheless, so wouldn’t the crackling still occur when pouring liquid over the “salt ice?”

    This will be easy enough to observe; I feel an experiment coming on.

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  21. exchemist Valued Senior Member

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    4F, perhaps?
     
  22. exchemist Valued Senior Member

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    Well yes, if it still has to expand significantly as a solid, before it reaches its melting point.

    But if, say, your salty ice cubes have a melting point of -15C and you get them out of a freezer thermostatted at -18C, then the only expansion the ice experiences before it melts is a temperature difference of a mere 3C, instead of the normal 18C. So what I'm saying is that it might easily contain the stress due to such a small amount of expansion, without cracking.

    (By the way, in the days of the feeble ice compartments in the 1960s fridges of my youth, we never heard ice crack. Nor did the cubes stick to your hand, the way they do when they are really cold out of a modern freezer. I expect the ice was only at about -5C or something, so there was little differential expansion before they just melted.)

    But yes, why not try it?
     
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  23. wegs Matter & Pixie Dust Valued Senior Member

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    Gotcha, understood! So this is why salt is used on icy roads during the winter months?
     

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