I like to understand that which one of the following items seems colder, when we touch them?
zero temperature ice
zero temperature water
Why?
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1$\begingroup$ Do you mean colder as in if you touch it what will you feel? If that is the case you have answered it yourself by listing them both at zero degrees (im assuming degrees C) $\endgroup$– TriatticusApr 18, 2015 at 20:00
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$\begingroup$ Also, are you talking about temperature in some energy sense? $\endgroup$– m0nhawkApr 18, 2015 at 20:08
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$\begingroup$ @ Dan, Yes, I mean this. But at one room, in winter, when you touch for example a metal chair and a wall you feel metal chair is colder (because of its conductivity), but both have same temperature. $\endgroup$– Mojtaba GolshaniApr 18, 2015 at 20:09
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$\begingroup$ This reminds me of the "Which is heavier, a pound of feathers or a pound of lead?" joke. I don't know if it's so simple, though. $\endgroup$– HDE 226868Apr 18, 2015 at 20:10
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2$\begingroup$ If you already know that metal feels colder than the wall because of conductivity, why don't you look up the conductivity of ice and water and answer this yourself? $\endgroup$– tpg2114Apr 18, 2015 at 20:24
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4 Answers
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The one that absorbs more heat from you will cool you more, and seem colder. But it isn't entirely straightforward.
If you pour water in your hand, water will flow to fit you. An ice cube will not make as good contact.
Water in contact with you will warm. It can then flow away and be replaced by fresh cold water. Ice doesn't flow
On the other hand, Ice at freezing will melt. This takes energy and leaves you with water at freezing.
Another point is that water is slightly denser than water. So for the same contact patch slightly more water is in contact with you than ice.
You are more likely to freeze to death in a rainstorm just above freezing than a snowstorm just below freezing. The rainstorm will soak your clothes and keep them from insulating. The snowstorm will leave you dry.
Edit - Latent heat of fusion
As suggested by Floris. See this Wikipedia article for more information.
Temperature is a measure of kinetic energy per molecule.
Water is a polar molecule. The H atoms in water have a slight positive charge, and the O atoms a negative charge. At low energy, this attraction gives rise to weak bonds, and ice forms.
As you raise the temperature, molecules vibrate harder. At a certain point (the melting temperature), vibrations are violent enough to begin breaking bonds. At this point, the temperature cannot rise. That is, if you add energy, the kinetic energy of the water molecules does not increase. Instead, you break more bonds, and this absorbs the extra energy.
When all the bonds are broken and all the the ice has melted, added energy once again goes into increasing the kinetic energy of water molecules.
It takes about 335 Joules to rupture all the bonds in 1 gram of ice. So the specific heat of fusion of ice is 335 J/g.
The latent heat of fusion is the amount of energy needed to rupture the bonds in whatever amount of ice you have on hand.
Since you are hotter than the ice, your molecules are have more energy than those in the ice. When you touch ice, your molecules bump into ice molecules and add energy to the ice. You lose energy and become cooler. Energy keeps flowing from you to the ice until the temperatures are equal. Thus it is important that melting ice is not warming as you cool.
answered Apr 18, 2015 at 21:05
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$\begingroup$ Valid points here. I would suggest adding something quantitative about latent heat of fusion for completeness $\endgroup$– FlorisApr 19, 2015 at 0:10
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$\begingroup$ Snow is mostly air, so it has less heat capacity. $\endgroup$ Jun 1, 2018 at 21:37
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I read some very technical answers here...mine is much more anecdotal and simple...when I had rotator cuff surgery in NYC at the Hospital For Special Surgery, I was prescribed a machine that circulated 'zero degrees WATER as opposed to an ice cuff', and told that it was more effective at reducing pain and inflammation because in that instance/use it 'acted colder' and 'had more effective full coverage of the treatment area'. 0 degrees is 0 degrees...but, if your question relates to therapeutic use...go with the zero degrees water and a compression sleeve.
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$\begingroup$ I think you explained this poorly. The machine that circulated water would remove more heat from your body because the water is circulated and thus fresh cold water is put in contact with you body. If you're just using an ice bag then the heat from you body diffuses into the water then must diffuse through a "thick" transition layer of water to the ice where it melts some of the ice. So all in all there the OP has a diffusion problem for which there isn't enough information to solve and give a definite answer. $\endgroup$– MaxWJun 1, 2018 at 22:06
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Since both are at the same temperature, both have the same degree of hotness ie. Temperature, hence similarly cold or hot. The difference is that water and ice both have different enthalpies, Water when converted to ice requires only phase change enthaply(assuming water to be at 273K), the enthalpy of freezing is then, Q(f) = ml
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How cold something feels, depends on how much thermal energy it makes us lose. This depends on a few factors:
- Specific heat capacity (how much energy it takes to heat up the material we touch)
- Thermal conductivity (how much of the energy we supply is led away from the surface we are in contact with)
- Atmospheric pressure (thermal conductivity increases in higher pressure, as the density of fluids will increase, leading to more thermal contact)
- Temperature difference
- Contact area (the bigger area that is in thermal contact, the more thermal conduction there will be)
- If the material moves (for instance, if you are lying still in a hot bath you will feel comfortable after a while, as the water closest to you will get closer to your body temperature, but if you start moving around, it will feel hotter again)
These are the most important factors I can think of.
Let's now look at water vs ice. Assume pressure and contact area are the same, for a fair comparison. Let's further assume that the water is perfectly still.
The important differences are
- Water heat capacity 4.19 J/(kg), ice 2.05 J/kg (link)
- Thermal conductivity water 0.56 W/(m⋅K), ice 2.18 W/(m⋅K) (link)
It takes more energy to heat up the water, but at least for water the temperature does rise as thermal energy is put in. Ice will remain at 0$^{o}$ C until it is melted (link). Ice is significantly more thermally conductive than water, meaning it will lead away more of the thermal energy to things that you are not in direct contact with.
Therefore, the ice will feel colder than the water.
In addition to this, there will be some convection currents in the water even if it starts out perfectly still. How much convection currents there will be depends on the shape of the water and the way you are in thermal contact with it. However, the temperature difference between you (37$^o$ C) and the water is not very large, so these currents would likely be small no matter what, and not impact the overall conclusion.
