Would planes sink into ice?
A number of readers have contacted us about the sensational information in the last issue documenting WW II planes covered with 75 metres (250 feet) of ice. Recalling the common school experiment in which a wire tensioned with weights ‘sinks’ through a block of ice, some wondered whether the planes could have sunk to that depth. However, the wire sinks through the ice in the experiment only if it is done at room temperature. Do the same experiment with the whole apparatus in a freezer, which would mimic the situation with the planes, and it does not work.1 The common explanation for the wire/ice experiment that the pressure of the wire melts the ice is wrong—such a device does not generate enough pressure to melt the ice. Heat transferred from the air in the room by the metallic wire, which is an efficient conductor of heat, melts the ice, which is a poor heat conductor, to allow the wire to ‘cut’ through.
So the planes could not have sunk through the ice; they were buried by the accumulation of snow (which becomes ice as it is compacted).
- We did this experiment. With a No.1 steel guitar string over an ice block about 40x25x25 mm (1.5x1x1″) in size and weighted with 4 kg (8.8 lbs) of water in two plastic milk bottles at room temperature, the wire cut through in 25 minutes, the ice re-freezing behind the cut. However, with the apparatus in a chest freezer, there was absolutely no movement in 8 hours. The pressure exerted by the wire? About 400 tonnes per square metre, which is enough to reduce the melting point of ice less than 0.5 degrees Celsius. As a matter of interest, a P-38 exerts a pressure of only 0.18 tonnes per square metre, enough to decrease the melting point about one five-thousandth of a degree.