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is "ice cube cutting wire" demo a misconception?



On Tue, 24 Feb 1998, Leigh Palmer wrote:

I don't think there is any doubt that the phenomenon of regelation
accounts for the wire cutting through the ice cube. After all, that
phenomenon occurs in a saturated water-ice environment. Only a small
pressure is needed to produce melting, and clearly the process of
refreezing (regelation) does take place; the ice is not cut.

Leigh,

I have serious doubts because of three other phenomena:

I have heard that ice melts below 0C if the curvature is concave, and so
clets and concavities tend to fill in. Ice melts above 0C if the
curvature of the ice is convex, and protuberances will melt at 0C. Both
holes and spikes are unstable, the water/ice interface "wants" to be a
plane, or at least a uniform sphere.

If an ice cube's temperature is below 0C, then when it is placed in
contact with another wet cube, the two will fuse together.

Changes in temperature propagate through metal wires at greater than
mm/sec speeds.

Because of the first, whenever the flat faces of two ice cubes are placed
together with water between them, the two ice cubes will fuse together.
Ditto for the second. Because of the third, a long wire with weights on
the end can easily melt ice if the environment is not at 0C or below.

To verify that the "wire pressure ice cutting" demo truely does as
advertized, "warm" ice near 0C internal temperature MUST be used. Next,
the cutting rate should be measured while the temperature of the
environment is varied. If the resulting graph of cutting rate suddenly
drops to zero for temperatures below 0C, then the demonstration is a
misconception. It actually may be a demonstration that flat faces of ice
easily fuse, that ice can be chilled below 0C (also causing fusion) and
that slightly-warm metal can move through ice very rapidly.

Ever put an ice cube on a big, finned aluminum heatsink? It "sinks
through the metal" like a television special effect. If the environment
of the "ice cutting" demo is not 0C, then we get the "miracle steak
thawing plate" effect, the wire outside the cube can easily be warmed by
the environment, and it rapidly delivers "thermal energy" (heh!) into the
length of wire within the cube.

Has anyone looked experimentally at the cutting-rate vs. temperature
curve? It probably has a big kink at 0C regardless, but the overall shape
of the curve would expose the truth.

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