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Ice cube mistery

  1. Jun 30, 2004 #1

    Clausius2

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    You know the hot weather we have here in Spain. So we have to use ice cubes when we drink water usually in summer in order to refresh a little ourselves. I would never recommend you to come here in summer if you are not an enemy.

    Well, some day I was pouring an ice cube (it almost had no water film in his surface) with a stainless steel spoon. As you can realise, the spoon temperature was greater than the ice cube one. I feel the ice cube sticked on the spoon surfice. Surely you have had this experience when you are not capable of unstick the ice cube although you move furiously the spoon.

    I wonder if this not agree with the second principle of thermodynamics. The proccess is:

    i) A thin water layer is formed in the ice surfice when it gets into contact with spoon surfice, because this one has higher temperature.

    ii) this water layer has to be frozen again in order to weld both bodies. And the heat has to come from the spoon or the ice cube.

    What is happening?. It seems more logical that all ice have to became liquid. It seems that I am cooling the spoon locally, although it has a greater temperature.

    I try to match this event with 2nd principle.
     
  2. jcsd
  3. Jun 30, 2004 #2
    hi

    it got stuck on the spoon because ur spoon is sticky. :surprise:
     
  4. Jun 30, 2004 #3

    russ_watters

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    I never thought about this before, but I would imagine that upon contact, heat is transferred pretty rapidly from the spoon to the ice. A thin layer of ice melts because it can't absorb the heat fast enough to prevent it. Once the ice has cooled the spoon enough, a temperature gradient is formed in the spoon and the ice (not very steep - the spoon will get very cold), with the part of the spoon touching the ice being at the same temperature of the ice - just below freezing.
     
  5. Jun 30, 2004 #4

    krab

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    Stainless steel is not a very good conductor of heat. Also, the initial temperature of the ice is significantly below freezing. Therefore, the S.S. spoon can locally cool to below freezing very quickly. Here's another effect. Gently press a stainless steel spoon, flat side down, on ice cream in a bowl. After a few seconds, the surface of the spoon freezes over very suddenly. At this point, the spoon sticks to the ice cream; in fact it can stick to your tongue too if you quickly transfer some ice cream with this (now very cold) spoon to your mouth.
     
  6. Jul 1, 2004 #5

    Clausius2

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    Well, all of you think the heat is transferred from spoon to ice cube every time of the proccess. The spoon is cooled locally because of this transferring, but I can't understand that the boundary layer just in the interface ice-spoon is frozen. We have concluded that is has to be frozen in order to make an active welding. If it would be in liquid state the ice would slip out of the spoon and fall to the floor (surely my mother would scold me :eek: ).

    If there is a heat flux trough this layer, I can't understand why this heat is not felt by the frozen water inside it. Somebody could think of this is the moment in which the layer is molten and the cube slips. But every of you can check (in your kitchen) that this time is very long (aprox. 5 minutes). I can't help thinking a part of the ice is being cooled, although is is in contact with a hotter surfice, which repulses the 2nd principle.

    Krab talks about stainless steel, but it is not a neccesary condition to employ this material.

    And "rush waters" describe it like a non-steady proccess, which is very logical. You say after a few moments both temperatures are below of freezing. Ok this explains the problem. But we could get into troubles if we talk about entropy.

    to be continue..
     
  7. Jul 1, 2004 #6
    Clausius2 me alegro mucho de encontrar a otro español por aquí. La respuesta a tu pregunta seguramente sea el rehielo.

    * Sorry for write in spanish, but always is interesting to proof that the world is so small ;)
     
  8. Jul 1, 2004 #7

    Clausius2

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    No te disculpes, que estos tienen que aprender español, que es uno de los idiomas más hablados en el mundo. Te he mandao un mensaje privado.



    "If I you want to be president of USA you will have to learn spanish".
    President Bush assistants.
    :biggrin:
     
  9. Jul 1, 2004 #8

    FZ+

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    Can I guess a different mechanism? My guess is that the spoon does not induce the ice cube to do the melting thing - the ice already has a thin layer of water around it, since it is always slowly melting. That is also why ice feels slippery in your hands. However, the presence of the spoon changes the environment of the water layer, which makes it freeze. (Possibly because of changing pressure, or something?) The heat is taken from the spoon, and the ice.
     
  10. Jul 2, 2004 #9

    Clausius2

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    Hey, do you ever have had a complete dry ice cube in your hands?. It is just the moment of getting it out of the freeze. It usually scticks on your fingers at this moments. When it has the water layer around its surface it's impossible that sticking occurs.


    I do not understand why a hotter body becomes to freeze the water layer. If the heat is taken from the spoon and the ice, then it would be a negative source of heating in the interface, and this is impossible.
     
  11. Jul 2, 2004 #10

    FZ+

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    My guess, and this is all speculation, is that the layer of water has to be just the right thickness - too thick, and it is thermodynamically impossible for it to freeze, too thin, and there is nothing to freeze. The analogy I am thinking of is the evaporation that takes place at the surface of liquid water - maybe something also happens at the edge of the ice? Perhaps even though the water is cold enough to freeze at this point...

    Well, one of the ways we can create cooling to reduce the pressure in a sealed container filled with hot water. The reduced pressure lowers the boiling point of the water, and causes the water to boil. This removes heat from the surroundings. I think. Maybe there is an equivalent in this case.

    Again, this is just speculation.
     
  12. Jul 2, 2004 #11

    turin

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    The ice cube is a very poor thermal conductor (eg. the igloo). Metals are relatively good thermal conductors (even steel). The layer of the ice closest to the spoon can be considerably warmer than the rest of the ice (i.e. the layer closest to the spoon can melt when heat is transfered from spoon to ice). Furthermore, I'm pretty sure that the spoon has a much lower specific heat capacity than the ice, so the temperature of the spoon will decrease far more than the average temperature of the ice will increase in this process. The end result (at least for a moment until both ice and spoon equalize with the ambient) is that the spoon transfers enough heat to drop its temperature down to 0oC. After this point (as the spoon continues to transfer heat into the ice), the temperature will only decrease further, and the layer of water that formed will refreeze.

    P.S. I feel so sorry for you having to put up with that nasty Spanish climate :cry:
     
  13. Jul 3, 2004 #12

    Clausius2

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    Your explanation seems very similar to the rush waters one. It seems the more understable I could imagine.

    PD: Surely Texas temperature is not so different. :devil:
     
  14. Jul 3, 2004 #13

    turin

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    Actually, I went straight to Yahoo! weather after I posted and looked at Madrid, Spain. It turns out that the temperatures are comparative, but Madrid ain't got nothin' on good ol' TX humidity. :tongue2:
     
  15. Jul 4, 2004 #14
    turin don't look at Madrid, Madrid is at 600 m ASL, and it's not so hot. Look at Sevilla or Cordoba ... we are in the hell. Last week, termometre never show less than 30 ºC even at night...

    Bye
     
  16. Jul 4, 2004 #15

    turin

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    MiGUi,
    I see. Are those towns on the southern coast?
     
  17. Jul 5, 2004 #16
    Well Sevilla and Cordoba are not at the coast, but a river goes through... so the humidity is not so big.

    I am from Vigo, a city in the northwest of Spain. The weather is not so warm, but is at the coast, and if you mix hot with humidity you want to die lol
     
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