Why does an ice-cube turn faster and faster while melting in water?
Whenever I put an ice-cube into a glass of hot water, so that it melts quickly, and it is initially rotating slowly, I noticed that its rotational speed increases as it melts and 'shrinks'. Why?
I thought of conservation of angular momentum, but does that really apply here? The part of the ice that melts into water would be 'carrying' off some of the ice-cube's angular momentum as it breaks away and diffuses into the surrounding water. So I see no reason for the remaining ice-cube to rotate faster.
I can only think of one possible reason, and it is just a guess: The friction between the water and ice causes the melting part to form eddies that spin in the opposite direction to the ice-cube, and so the ice-cube loses much less momentum in melting since its boundary is actually moving together with the adjacent eddy boundaries. If the eddies expand as the ice-cube shrinks, it seems we would have to conclude that the ice-cube must rotate faster to preserve total angular momentum.
But such an analysis seems very weird, and cannot be a proper picture of what is really happening, since the 'number' of eddies must decrease as the ice-cube shrinks, so they must combine in some manner, and I have no idea how any of this works out.
So, what really is spinning the ice?
classical-mechanics fluid-dynamics angular-momentum rotational-dynamics ice
asked 5 hours ago
user21820
1,415914
add a comment |
Whenever I put an ice-cube into a glass of hot water, so that it melts quickly, and it is initially rotating slowly, I noticed that its rotational speed increases as it melts and 'shrinks'. Why?
I thought of conservation of angular momentum, but does that really apply here? The part of the ice that melts into water would be 'carrying' off some of the ice-cube's angular momentum as it breaks away and diffuses into the surrounding water. So I see no reason for the remaining ice-cube to rotate faster.
I can only think of one possible reason, and it is just a guess: The friction between the water and ice causes the melting part to form eddies that spin in the opposite direction to the ice-cube, and so the ice-cube loses much less momentum in melting since its boundary is actually moving together with the adjacent eddy boundaries. If the eddies expand as the ice-cube shrinks, it seems we would have to conclude that the ice-cube must rotate faster to preserve total angular momentum.
But such an analysis seems very weird, and cannot be a proper picture of what is really happening, since the 'number' of eddies must decrease as the ice-cube shrinks, so they must combine in some manner, and I have no idea how any of this works out.
So, what really is spinning the ice?
classical-mechanics fluid-dynamics angular-momentum rotational-dynamics ice
asked 5 hours ago
user21820
1,415914
A video of the ice cubes melting/spinning would be useful
– binaryfunt
5 hours ago
Whenever I have observed this phenomenon, I've thought it was correlated with air bubbles near the white center of the cube breaching the surface of the ice, rather than with the transparent solid ice near the edges of a fresh cube. A video would help to confirm that everyone is discussing the same effect.
– rob♦
31 mins ago
@rob: I don't have the tools to make a proper video, but I don't think it's difficult to reproduce. My ice is made from rather pure boiled water but it does have air bubbles trapped in it. Even if air bubbles breach the surface of the ice (which they do in my case), how could it cause the ice to rotate faster? That is what I cannot understand. Either the rotational momentum is not taken away by whatever is leaving the ice (whether melted water or air) sufficiently, or the energy from the heat gradient is contributing, such as Lewis Miller suggests.
– user21820
4 mins ago
My ice-cube is also not cube-shaped (due to the ice-tray) but look like this without the ice spike. I doubt that the air bubbles are trapped in some intrinsically asymmetric way such that their escape imparts a non-negligible torque.
– user21820
1 min ago
@user21820 I'm thinking of the history of the Mpemba effect, which involved centuries of very smart people using the same words to talk about slightly different things, which made it impossible to decide whether the phenomenon of interest was real or not.
– rob♦
55 secs ago
add a comment |
Whenever I put an ice-cube into a glass of hot water, so that it melts quickly, and it is initially rotating slowly, I noticed that its rotational speed increases as it melts and 'shrinks'. Why?
I thought of conservation of angular momentum, but does that really apply here? The part of the ice that melts into water would be 'carrying' off some of the ice-cube's angular momentum as it breaks away and diffuses into the surrounding water. So I see no reason for the remaining ice-cube to rotate faster.
I can only think of one possible reason, and it is just a guess: The friction between the water and ice causes the melting part to form eddies that spin in the opposite direction to the ice-cube, and so the ice-cube loses much less momentum in melting since its boundary is actually moving together with the adjacent eddy boundaries. If the eddies expand as the ice-cube shrinks, it seems we would have to conclude that the ice-cube must rotate faster to preserve total angular momentum.
But such an analysis seems very weird, and cannot be a proper picture of what is really happening, since the 'number' of eddies must decrease as the ice-cube shrinks, so they must combine in some manner, and I have no idea how any of this works out.
So, what really is spinning the ice?
classical-mechanics fluid-dynamics angular-momentum rotational-dynamics ice
asked 5 hours ago
user21820
1,415914
Whenever I put an ice-cube into a glass of hot water, so that it melts quickly, and it is initially rotating slowly, I noticed that its rotational speed increases as it melts and 'shrinks'. Why?
I thought of conservation of angular momentum, but does that really apply here? The part of the ice that melts into water would be 'carrying' off some of the ice-cube's angular momentum as it breaks away and diffuses into the surrounding water. So I see no reason for the remaining ice-cube to rotate faster.
I can only think of one possible reason, and it is just a guess: The friction between the water and ice causes the melting part to form eddies that spin in the opposite direction to the ice-cube, and so the ice-cube loses much less momentum in melting since its boundary is actually moving together with the adjacent eddy boundaries. If the eddies expand as the ice-cube shrinks, it seems we would have to conclude that the ice-cube must rotate faster to preserve total angular momentum.
But such an analysis seems very weird, and cannot be a proper picture of what is really happening, since the 'number' of eddies must decrease as the ice-cube shrinks, so they must combine in some manner, and I have no idea how any of this works out.
So, what really is spinning the ice?
classical-mechanics fluid-dynamics angular-momentum rotational-dynamics ice
classical-mechanics fluid-dynamics angular-momentum rotational-dynamics ice
asked 5 hours ago
user21820
1,415914
asked 5 hours ago
user21820
1,415914
asked 5 hours ago
user21820
1,415914
asked 5 hours ago
user21820
1,415914
asked 5 hours ago
user21820
1,415914
1,415914
A video of the ice cubes melting/spinning would be useful
– binaryfunt
5 hours ago
Whenever I have observed this phenomenon, I've thought it was correlated with air bubbles near the white center of the cube breaching the surface of the ice, rather than with the transparent solid ice near the edges of a fresh cube. A video would help to confirm that everyone is discussing the same effect.
– rob♦
31 mins ago
@rob: I don't have the tools to make a proper video, but I don't think it's difficult to reproduce. My ice is made from rather pure boiled water but it does have air bubbles trapped in it. Even if air bubbles breach the surface of the ice (which they do in my case), how could it cause the ice to rotate faster? That is what I cannot understand. Either the rotational momentum is not taken away by whatever is leaving the ice (whether melted water or air) sufficiently, or the energy from the heat gradient is contributing, such as Lewis Miller suggests.
– user21820
4 mins ago
My ice-cube is also not cube-shaped (due to the ice-tray) but look like this without the ice spike. I doubt that the air bubbles are trapped in some intrinsically asymmetric way such that their escape imparts a non-negligible torque.
– user21820
1 min ago
@user21820 I'm thinking of the history of the Mpemba effect, which involved centuries of very smart people using the same words to talk about slightly different things, which made it impossible to decide whether the phenomenon of interest was real or not.
– rob♦
55 secs ago
add a comment |
A video of the ice cubes melting/spinning would be useful
– binaryfunt
5 hours ago
Whenever I have observed this phenomenon, I've thought it was correlated with air bubbles near the white center of the cube breaching the surface of the ice, rather than with the transparent solid ice near the edges of a fresh cube. A video would help to confirm that everyone is discussing the same effect.
– rob♦
31 mins ago
@rob: I don't have the tools to make a proper video, but I don't think it's difficult to reproduce. My ice is made from rather pure boiled water but it does have air bubbles trapped in it. Even if air bubbles breach the surface of the ice (which they do in my case), how could it cause the ice to rotate faster? That is what I cannot understand. Either the rotational momentum is not taken away by whatever is leaving the ice (whether melted water or air) sufficiently, or the energy from the heat gradient is contributing, such as Lewis Miller suggests.
– user21820
4 mins ago
My ice-cube is also not cube-shaped (due to the ice-tray) but look like this without the ice spike. I doubt that the air bubbles are trapped in some intrinsically asymmetric way such that their escape imparts a non-negligible torque.
– user21820
1 min ago
@user21820 I'm thinking of the history of the Mpemba effect, which involved centuries of very smart people using the same words to talk about slightly different things, which made it impossible to decide whether the phenomenon of interest was real or not.
– rob♦
55 secs ago
A video of the ice cubes melting/spinning would be useful
– binaryfunt
5 hours ago
A video of the ice cubes melting/spinning would be useful
– binaryfunt
5 hours ago
Whenever I have observed this phenomenon, I've thought it was correlated with air bubbles near the white center of the cube breaching the surface of the ice, rather than with the transparent solid ice near the edges of a fresh cube. A video would help to confirm that everyone is discussing the same effect.
– rob♦
31 mins ago
Whenever I have observed this phenomenon, I've thought it was correlated with air bubbles near the white center of the cube breaching the surface of the ice, rather than with the transparent solid ice near the edges of a fresh cube. A video would help to confirm that everyone is discussing the same effect.
– rob♦
31 mins ago
@rob: I don't have the tools to make a proper video, but I don't think it's difficult to reproduce. My ice is made from rather pure boiled water but it does have air bubbles trapped in it. Even if air bubbles breach the surface of the ice (which they do in my case), how could it cause the ice to rotate faster? That is what I cannot understand. Either the rotational momentum is not taken away by whatever is leaving the ice (whether melted water or air) sufficiently, or the energy from the heat gradient is contributing, such as Lewis Miller suggests.
– user21820
4 mins ago
@rob: I don't have the tools to make a proper video, but I don't think it's difficult to reproduce. My ice is made from rather pure boiled water but it does have air bubbles trapped in it. Even if air bubbles breach the surface of the ice (which they do in my case), how could it cause the ice to rotate faster? That is what I cannot understand. Either the rotational momentum is not taken away by whatever is leaving the ice (whether melted water or air) sufficiently, or the energy from the heat gradient is contributing, such as Lewis Miller suggests.
– user21820
4 mins ago
My ice-cube is also not cube-shaped (due to the ice-tray) but look like this without the ice spike. I doubt that the air bubbles are trapped in some intrinsically asymmetric way such that their escape imparts a non-negligible torque.
– user21820
1 min ago
My ice-cube is also not cube-shaped (due to the ice-tray) but look like this without the ice spike. I doubt that the air bubbles are trapped in some intrinsically asymmetric way such that their escape imparts a non-negligible torque.
– user21820
1 min ago
@user21820 I'm thinking of the history of the Mpemba effect, which involved centuries of very smart people using the same words to talk about slightly different things, which made it impossible to decide whether the phenomenon of interest was real or not.
– rob♦
55 secs ago
@user21820 I'm thinking of the history of the Mpemba effect, which involved centuries of very smart people using the same words to talk about slightly different things, which made it impossible to decide whether the phenomenon of interest was real or not.
– rob♦
55 secs ago
add a comment |
1 Answer
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The same physics that explains why water tends to rotate when you drain your bathtub also answers this question. In both situations there is a downward flow of water that accentuates the residual rotation that remains after the vessel has been filled. In the case of your bathtub the downward flow results from opening the drain. For the ice cube in hot water the downward flow is created when the just melted water sinks because it is colder than the surrounding water. Since the ice cube is getting smaller, it is easier to rotate in the whirlpool that is created (by the melting process) and it thereby tends to rotate faster.
There is an urban legend that claims that the direction of spin in drains is associated with the coriolis effect and differs between the northern and southern hemispheres. While this may be true of hurricanes and cyclones, it is too small an effect to apply to bathtub drains or glasses of hot water with ice cubes. For these smaller scale systems the rotation direction is dictated by the residual rotation created when the vessel was filled. This small residual rotation may not be noticable until the downward flow accentuates it.
answered 2 hours ago
Lewis Miller
3,9971920
So you're saying that the temperature gradient is powering the whirlpool. It would be interesting to see visual evidence of such a motion in the water melting off a dyed ice-cube. I only noticed this effect when the water was relatively hot, so your suggestion is actually quite plausible.
– user21820
1 hour ago
Two more "not a questions" 1. geometry(when ice melt, it geometric shape change from a cubic to more likely a slim of ice, which made the original rotational axis become the one(of two) that easily to be rotated.) 2. I still a little bit suspicious about the main cause to be "current" caused by the diffusion. I was thinking maybe rotational momentum was conserved because melting did not do a good job at taking away rotational momentum.(The rotational energy was taken away by the fraction force, but not melting)
– user9976437
42 mins ago
For a sense of the scale of the Coriolis effect in a human-sized water vessel, see these synchronized multi-hemispheric videos.
– rob♦
7 mins ago
add a comment |
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1 Answer
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The same physics that explains why water tends to rotate when you drain your bathtub also answers this question. In both situations there is a downward flow of water that accentuates the residual rotation that remains after the vessel has been filled. In the case of your bathtub the downward flow results from opening the drain. For the ice cube in hot water the downward flow is created when the just melted water sinks because it is colder than the surrounding water. Since the ice cube is getting smaller, it is easier to rotate in the whirlpool that is created (by the melting process) and it thereby tends to rotate faster.
There is an urban legend that claims that the direction of spin in drains is associated with the coriolis effect and differs between the northern and southern hemispheres. While this may be true of hurricanes and cyclones, it is too small an effect to apply to bathtub drains or glasses of hot water with ice cubes. For these smaller scale systems the rotation direction is dictated by the residual rotation created when the vessel was filled. This small residual rotation may not be noticable until the downward flow accentuates it.
answered 2 hours ago
Lewis Miller
3,9971920
So you're saying that the temperature gradient is powering the whirlpool. It would be interesting to see visual evidence of such a motion in the water melting off a dyed ice-cube. I only noticed this effect when the water was relatively hot, so your suggestion is actually quite plausible.
– user21820
1 hour ago
Two more "not a questions" 1. geometry(when ice melt, it geometric shape change from a cubic to more likely a slim of ice, which made the original rotational axis become the one(of two) that easily to be rotated.) 2. I still a little bit suspicious about the main cause to be "current" caused by the diffusion. I was thinking maybe rotational momentum was conserved because melting did not do a good job at taking away rotational momentum.(The rotational energy was taken away by the fraction force, but not melting)
– user9976437
42 mins ago
For a sense of the scale of the Coriolis effect in a human-sized water vessel, see these synchronized multi-hemispheric videos.
– rob♦
7 mins ago
add a comment |
The same physics that explains why water tends to rotate when you drain your bathtub also answers this question. In both situations there is a downward flow of water that accentuates the residual rotation that remains after the vessel has been filled. In the case of your bathtub the downward flow results from opening the drain. For the ice cube in hot water the downward flow is created when the just melted water sinks because it is colder than the surrounding water. Since the ice cube is getting smaller, it is easier to rotate in the whirlpool that is created (by the melting process) and it thereby tends to rotate faster.
There is an urban legend that claims that the direction of spin in drains is associated with the coriolis effect and differs between the northern and southern hemispheres. While this may be true of hurricanes and cyclones, it is too small an effect to apply to bathtub drains or glasses of hot water with ice cubes. For these smaller scale systems the rotation direction is dictated by the residual rotation created when the vessel was filled. This small residual rotation may not be noticable until the downward flow accentuates it.
answered 2 hours ago
Lewis Miller
3,9971920
So you're saying that the temperature gradient is powering the whirlpool. It would be interesting to see visual evidence of such a motion in the water melting off a dyed ice-cube. I only noticed this effect when the water was relatively hot, so your suggestion is actually quite plausible.
– user21820
1 hour ago
Two more "not a questions" 1. geometry(when ice melt, it geometric shape change from a cubic to more likely a slim of ice, which made the original rotational axis become the one(of two) that easily to be rotated.) 2. I still a little bit suspicious about the main cause to be "current" caused by the diffusion. I was thinking maybe rotational momentum was conserved because melting did not do a good job at taking away rotational momentum.(The rotational energy was taken away by the fraction force, but not melting)
– user9976437
42 mins ago
For a sense of the scale of the Coriolis effect in a human-sized water vessel, see these synchronized multi-hemispheric videos.
– rob♦
7 mins ago
add a comment |
The same physics that explains why water tends to rotate when you drain your bathtub also answers this question. In both situations there is a downward flow of water that accentuates the residual rotation that remains after the vessel has been filled. In the case of your bathtub the downward flow results from opening the drain. For the ice cube in hot water the downward flow is created when the just melted water sinks because it is colder than the surrounding water. Since the ice cube is getting smaller, it is easier to rotate in the whirlpool that is created (by the melting process) and it thereby tends to rotate faster.
There is an urban legend that claims that the direction of spin in drains is associated with the coriolis effect and differs between the northern and southern hemispheres. While this may be true of hurricanes and cyclones, it is too small an effect to apply to bathtub drains or glasses of hot water with ice cubes. For these smaller scale systems the rotation direction is dictated by the residual rotation created when the vessel was filled. This small residual rotation may not be noticable until the downward flow accentuates it.
answered 2 hours ago
Lewis Miller
3,9971920
The same physics that explains why water tends to rotate when you drain your bathtub also answers this question. In both situations there is a downward flow of water that accentuates the residual rotation that remains after the vessel has been filled. In the case of your bathtub the downward flow results from opening the drain. For the ice cube in hot water the downward flow is created when the just melted water sinks because it is colder than the surrounding water. Since the ice cube is getting smaller, it is easier to rotate in the whirlpool that is created (by the melting process) and it thereby tends to rotate faster.
There is an urban legend that claims that the direction of spin in drains is associated with the coriolis effect and differs between the northern and southern hemispheres. While this may be true of hurricanes and cyclones, it is too small an effect to apply to bathtub drains or glasses of hot water with ice cubes. For these smaller scale systems the rotation direction is dictated by the residual rotation created when the vessel was filled. This small residual rotation may not be noticable until the downward flow accentuates it.
answered 2 hours ago
Lewis Miller
3,9971920
edited 1 hour ago
answered 2 hours ago
Lewis Miller
3,9971920
answered 2 hours ago
Lewis Miller
3,9971920
answered 2 hours ago
Lewis Miller
3,9971920
3,9971920
So you're saying that the temperature gradient is powering the whirlpool. It would be interesting to see visual evidence of such a motion in the water melting off a dyed ice-cube. I only noticed this effect when the water was relatively hot, so your suggestion is actually quite plausible.
– user21820
1 hour ago
Two more "not a questions" 1. geometry(when ice melt, it geometric shape change from a cubic to more likely a slim of ice, which made the original rotational axis become the one(of two) that easily to be rotated.) 2. I still a little bit suspicious about the main cause to be "current" caused by the diffusion. I was thinking maybe rotational momentum was conserved because melting did not do a good job at taking away rotational momentum.(The rotational energy was taken away by the fraction force, but not melting)
– user9976437
42 mins ago
For a sense of the scale of the Coriolis effect in a human-sized water vessel, see these synchronized multi-hemispheric videos.
– rob♦
7 mins ago
add a comment |
So you're saying that the temperature gradient is powering the whirlpool. It would be interesting to see visual evidence of such a motion in the water melting off a dyed ice-cube. I only noticed this effect when the water was relatively hot, so your suggestion is actually quite plausible.
– user21820
1 hour ago
Two more "not a questions" 1. geometry(when ice melt, it geometric shape change from a cubic to more likely a slim of ice, which made the original rotational axis become the one(of two) that easily to be rotated.) 2. I still a little bit suspicious about the main cause to be "current" caused by the diffusion. I was thinking maybe rotational momentum was conserved because melting did not do a good job at taking away rotational momentum.(The rotational energy was taken away by the fraction force, but not melting)
– user9976437
42 mins ago
For a sense of the scale of the Coriolis effect in a human-sized water vessel, see these synchronized multi-hemispheric videos.
– rob♦
7 mins ago
So you're saying that the temperature gradient is powering the whirlpool. It would be interesting to see visual evidence of such a motion in the water melting off a dyed ice-cube. I only noticed this effect when the water was relatively hot, so your suggestion is actually quite plausible.
– user21820
1 hour ago
So you're saying that the temperature gradient is powering the whirlpool. It would be interesting to see visual evidence of such a motion in the water melting off a dyed ice-cube. I only noticed this effect when the water was relatively hot, so your suggestion is actually quite plausible.
– user21820
1 hour ago
Two more "not a questions" 1. geometry(when ice melt, it geometric shape change from a cubic to more likely a slim of ice, which made the original rotational axis become the one(of two) that easily to be rotated.) 2. I still a little bit suspicious about the main cause to be "current" caused by the diffusion. I was thinking maybe rotational momentum was conserved because melting did not do a good job at taking away rotational momentum.(The rotational energy was taken away by the fraction force, but not melting)
– user9976437
42 mins ago
Two more "not a questions" 1. geometry(when ice melt, it geometric shape change from a cubic to more likely a slim of ice, which made the original rotational axis become the one(of two) that easily to be rotated.) 2. I still a little bit suspicious about the main cause to be "current" caused by the diffusion. I was thinking maybe rotational momentum was conserved because melting did not do a good job at taking away rotational momentum.(The rotational energy was taken away by the fraction force, but not melting)
– user9976437
42 mins ago
For a sense of the scale of the Coriolis effect in a human-sized water vessel, see these synchronized multi-hemispheric videos.
– rob♦
7 mins ago
For a sense of the scale of the Coriolis effect in a human-sized water vessel, see these synchronized multi-hemispheric videos.
– rob♦
7 mins ago
add a comment |
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A video of the ice cubes melting/spinning would be useful
– binaryfunt
5 hours ago
Whenever I have observed this phenomenon, I've thought it was correlated with air bubbles near the white center of the cube breaching the surface of the ice, rather than with the transparent solid ice near the edges of a fresh cube. A video would help to confirm that everyone is discussing the same effect.
– rob♦
31 mins ago
@rob: I don't have the tools to make a proper video, but I don't think it's difficult to reproduce. My ice is made from rather pure boiled water but it does have air bubbles trapped in it. Even if air bubbles breach the surface of the ice (which they do in my case), how could it cause the ice to rotate faster? That is what I cannot understand. Either the rotational momentum is not taken away by whatever is leaving the ice (whether melted water or air) sufficiently, or the energy from the heat gradient is contributing, such as Lewis Miller suggests.
– user21820
4 mins ago
My ice-cube is also not cube-shaped (due to the ice-tray) but look like this without the ice spike. I doubt that the air bubbles are trapped in some intrinsically asymmetric way such that their escape imparts a non-negligible torque.
– user21820
1 min ago
@user21820 I'm thinking of the history of the Mpemba effect, which involved centuries of very smart people using the same words to talk about slightly different things, which made it impossible to decide whether the phenomenon of interest was real or not.
– rob♦
55 secs ago