Supercooled water immedaitely freezes to ice when a tiny ice is touched to it.How is it possible?
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Now that it's been freezing outside for the last few days, I experimented a bit with supercooling. I've left a bottle of clean water outside for a few hours, and behold, when I shook the bottle, the liquid began to freeze rapidly, as expected.   However, not all of the water froze, only about half of it. This got me thinking.  I reasoned that happens because freezing releases heat, and that heat raises the temperature of the ice and remaning water to 0$^\circ$C, at which point the freezing stops.  To try to quantify this, set   $H_f = 334000 \frac{J}{kg}$, the "freezing heat" (enthalpy of fusion) of ice, $c_i = 2110 \frac{J}{kg\cdot K}$, specific heat of ice, $c_w = 4181 \frac{J}{kg\cdot K}$, specific heat of water, $M$, initial mass of supercooled water, $T_0$, initial temperature of supercooled water, $m$, mass of ice at a given moment, $T$, temperature at a given moment.   We suppose that the energy released by the freezing of a $\textrm dm$ mass of ice is used up by raising the temperature of both the already frozen ice ($m$) and the remaining water ($M-m$):  $$ \textrm dm \cdot H_f = c_i m \cdot\textrm dT + (M-m)c_w \cdot\textrm dT$$  By rearranging we get a linear differential equation for $m(T)$:  $$\frac{\textrm dm}{\textrm dT}+\frac{c_w-c_i}{H_f}m = \frac{c_w}{H_f}M$$  The solution of this equation, using the initial condition that at $T=T_0$, $m=0$:  $$ m = M \frac{c_w}{c_w-c_i}\left[ 1-e^{-\frac{c_w-c_i}{H_f}(T-T_0)} \right]$$  This looks neat, however, plugging in the actual values of the constants, $T = 0^\circ$C and $T_0 = -6^\circ$C, I get that little more than 7% of the water should freeze - as opposed to more than half, as I've observed. What's worse, the formula can be used to calculate the starting temperature required to freeze all the supercooled water: $$T_{all} = \frac{H_f \log\frac{c_w}{c_i}}{c_i-c_w}=-110.26^\circ \textrm C$$ which seems absurd.  Where is the error in the calculation above?  I've made a number of assumptions which may or may not hold:   the constants are really constant. I think this is a good approximation for $c_w$, a not that good but still acceptable approximation for $c_i$, and I suppose it holds to $H_f$ to some extent as well. there is no heat transfer with the environment, i.e. the bottle is a closed system. The process seemed fast enough (a few seconds at most) for this to be a good approximation. the system is in a thermal equilibrium at all times and the heat released by the freezing of the ice is distributed evenly in the emerging ice-water mixture. Now this is where I have doubts. Precisely because of the process happening so fast, this might not be true at all. However, acknowledging the presence of temperature variations makes the problem order of magnitudes harder: one has to solve a system of partial differential equations that take heat transfer, the shape of the bottle and \$deity knows what else into account.
110115
So with this "arctic blast" continuing, I've noticed that for my area, the temperature drops below freezing just long enough to cause freezing rain, but then the sun comes out and the temperature rises immediately. However, on bridges, ice continues to form.   How can ice form even if the temperature is above freezing?
85280
Is this really possible? Is there any other example of this other than the Koch Snowflake? If so can you prove that example to be true?
95050
the teacher gave me this problem to solve. So i hope you can help me with it. Here is the problem: John poured 150ml ob boiling water in 2 cups made out of polystyrene. Cups are open on the top so heat goes out there. Temperature of the outside air is 20°C. In 1 cup he add 5 mm thick layer of hot oil. He measured starting temperatures and then he measured temperatures again after 10 min. He measured the mass of water and water+oil before and after 10 min.  Here are the resaults:   -cup 1 (only water)  starting temp: 96°C  finnish temp: 64°C  starting mass: 149.4g  finnish mass: 142.42g  -cup 2(with oil on top)  starting temp.: 96°C  finnish temp.:91°C  starting mass: 164.72g  finnish mass: 164.70g  The surface of the both cups is 0.003 m2  Questions: 1.Why did the water covered with oil cooled down slower that the one with no oil? Show with calculations. 2.Why did John use oil with temperature around 100°C and not oil with room temperature? How would the resaults change if he used room temeprature oil? 3. Which other physical values, which are relevant, can you calculate from this informations? Basiccaly i need the physics behing why does this happen.
46493
So  i have a scene with a few objects, and a water simulation in the scene. However I want to animate the camera turning around in the scene, while the water simulation is frozen in time. So something like a time freeze effect. But when ever I try to render an animation it renders the water simulation too. I just need one frame of the water simulation. Is there a way to do this?
124138
Yesterday my friends and I were solving this easy-looking question:  A metal cube is placed in an empty vessel. When water is filled in the vessel  so that the cube is completely immersed in the water, the force on the bottom of the vessel in contact with the cube: (A) Will Increase (B) Will Decrease (C) Will remain the same (D) Will become zero  At first we thought the answer to be (B) considering the buoyant force acting opposite to the weight of the cube. But then, a question popped up in my mind: &quot;What causes this buoyant force even if no fluid was actually displaced?&quot; So I referred to the Archimedes' Statement:  Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. — Archimedes of Syracuse  But according to the question, no such fluid was displaced by the block ! So, here are my questions:  What is the basic reason behind buoyancy? Is it the pressure difference in fluids or the 'liquid-displaced' theory?  What must be the answer to the question (That I was solving) ?  Considering the case that you may say- &quot;The reason behind buoyancy is the pressure difference in the fluids&quot;; Will there be no buoyant force applied to the iron cube as there is no fluid layer present below the cube i.e. no pressure difference?   (Considering the iron cube is VERY dense and thus not allowing any fluid layer to push its way below it)  Or you might add another statement to the above question that-&quot;Yes, buoyant force is applied as there is always a fluid layer present below it...&quot; .Please do explain yourself.  If your answer is according to the Principle given by Archimedes of Syracuse , will there be no buoyant force on the cube as the cube didn't actually displace any fluid? Just like the case where you may consider it to be a part of the vessel itself.
638
I took apart my cooling platform Something like this :  And I found something like this inside :       I wonder why around the hollows are the "canyon like" structures.  PS: I also drop this platform on the floor, maybe this could be a reason ?   EDIT :  Everybody seems (except Brandon Enright answer) to ignore the word "dust" in this question. Those structures are not in the plastic itself. It is dust ON the plastic.  Proof :     Completely wiped out with my finger :
8999
I read that the soda's temperature allows it to contain its $\text{CO}_2$: colder means it can retain its bubbles better.  So, why does soda fizz when it meets ice?  If anything, because the soda is made colder, it should retain its gas better, as per above. The ice is taking away energy from the soda, thus freezing. Won't heating, not freezing, encourage the gas to escape, or is it not an energy matter?
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So, I just was trying to get back into blender, and I made .  Unfortunately, this cup has some issues right at the bottom of the inside, and I can't figure out why.  You can download the blend file .  And just for good measure, here is a screenshot of the problem.
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My setup:   plastic box (~1l) with the cover painted black mat the bottom of the box covered with sponges saturated with ethyl alcohol (90%) to the limit (all over sponge capacity poured back to bottle) turned upside down and placed on ~0.5kg of dry ice.   I can see a 'rain' of particles of alcohol, but no traces.  I disassembled smoke detector and attached the sample of americium to the box. No effect.  Here is the 'rain':   Here are some pictures of the setup:          Any help appreciated.
20915
At xmas, I had a cup of tea with some debris at the bottom from the leaves.  With less than an inch of tea left, I'd shake the cup to get a little vortex going, then stop shaking and watch it spin.  At first, the particles were dispersed fairly evenly throughout the liquid, but as time went on (and the vortex slowed, although I don't know if it's relevant) the particles would collect in the middle, until, by the time the liquid appeared to almost no longer be turning, all the little bits were collected in this nice neat pile in the center.  What's the physical explanation of the accumulation of particles in the middle?  My guess is that it's something to do with a larger radius costing the particles more work through friction...
45069
I was reading about growing single crystals and I'm a little confused about this -  In most crystal growing processes, a "seed crystal" is used, and the rest of the material crystallizes on the seed crystal (for example the ).   But thinking about entropy, wouldn't it be more favourable for the vapour/liquid to not crystallize and hence maintain a larger disorder?   A similar process occurs in supersaturated vapour as well, where a small liquid droplet acts as a "seed" for more condensation to occur. So I suspect I'm missing something, but I can't figure out what.
33179
I have been having a discussion regarding the Shape Water cantrip from the Elemental Evil Player's Companion. A friend and I are trying to come to an accurate view of how this spell actually functions.   Some example questions:   Must the targeted water be within a 5 foot cube area, or does it need to be of a volume not exceeding 125 cubic feet? If you shape water that is within a 5 foot cube, can the final shape you animate it to extend outside the cube? Can you cause the shaping to affect ice and snow, or only liquid water? Would you be able to carry a globe of water alongside you over distances?   Really, there are two parts:    What can be targeted by the spell? What are the limitations on the 'shape and animate' portion of the spell?   The answer I am looking for, if possible, would use the language of the spell, possibly with precedent from other game text, to clearly define the limitations of this cantrip.
115768
I created a room, and now it's frozen due to inactivity.  How can I unfreeze it?
97189
I'm having a discussion with someone. I said that it is -even theoretically- impossible to reach $0$ K, because that would imply that all molecules in the substance would stand perfectly still.  He said that this isn't true, because my theory violates energy-time uncertainty principle. He also told me to look up the Schrödinger equation and solve it for an oscillator approximating a molecule. See that it's lowest energy state is still non-zero.  Is he right in saying this and if so, can you explain me a bit better what he is talking about.
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I read that contrails can only form if the outside temperature is below -40 degree Celsius. But why not earlier? Water is already super-cooled below 0 degree Celsius. If a condensation nuclei touches the water, it will instantly freeze, from what I understood from :  Contrails form at -40 degrees Fahrenheit (which is also -40 Celsius), or colder. At that temperature the tiny drops of condensed water will instantly freeze.  Now, an aircraft outputs lots of soot, that can also act as condensation nuclei. So, why aren't contrails forming at 0 degree Celsius already? EDIT: For example, let's just take a look at this weather balloon data: ----------------------------------------------------------------------------- PRES   HGHT   TEMP   DWPT   RELH    hPa     m      C      C      %     ----------------------------------------------------------------------------- 955.0    614    3.4   -0.6   75    932.0    812    2.2   -2.0   74    925.0    873    1.8   -2.4   74    885.0   1227   -0.3   -5.3   69    850.0   1548   -3.3   -6.2   80    842.0   1622   -4.0   -6.6   82    797.0   2051   -7.8   -8.9   92    781.0   2209   -9.2   -9.8   96    769.0   2330  -10.3  -10.4   99     As we can see, the temperature at a pressure altitude of 769, what is 2330 meter on that day, is -10 degree and the relative humidity is 99%. My question is: Why can't contrails form in this condition? Or can they? Because the air is very humid and the engine's vapor would give it the rest to be over-saturated, what makes the water vapor condense on the soot. And the temperature would freeze them. Every internet source says, they can only exist at or below -40 degree Celsius. But what about this condition? What stops them to form at this temperature and humidity? I need to know this, because I'm writing my pre-scientific work about it. I understand contrail formation pretty much so far, but some small puzzle parts are still missing.
24129
I think everyone should have seen a bowl of hot water moving by itself on a flat surface such as glass(seems like it is moving by itself but maybe there are some external force applied to it when it moves). What is the explanation of this phenomenon?  Hypotheses :   Since the bowl is heavy, for it to move the friction between the bowl and the surface must be very very low. I have heard that water may form a thin layer between the bowl and the surface, but l'm not sure whether it is the case or not. I think the bowl can move by itself because heat makes the air below the bowl expand.   Edit : I will re-experiment those again and update the question in few days. Maybe I will take a video clip too. and I am not talking about a magic trick whatsoever.