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Tuesday, December 02, 2003

On opening envelopes with your finger instead of a knife -  

Two physicists have recently worked out why it's harder to open an envelope with your finger than with a knife (see here for the ref but you will, probably need a subscription to Physical Review Letters). The basic idea is that if you use a relatively thin tool (where thin has to do with the qualities of the thing you're trying to cut) you create an even, regular crack.

If you use a thicker tool, however, its harder to push the tool through the recently created crack. In an attempt to accommodate the tool a stair step (or a sort of rounded stair step) pattern is created. This pattern means that the edge of the envelope is likely to be frayed and that the whole process will take more energy.

Why is this important if you're not particularly interested in envelopes? Good question. The authors also suggest that the same sort of physics may explain the patterns often visible at the edges of moving ice sheets/glaciers. Detailed knowledge of the forces stopping ice from flowing is critical if we're going to understand when, for example, the West Antarctic ice sheet might fail and the resulting sea level rise flood Florida (not necessarily a bad thing if my Grandmother has already been evacuated).
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