Submitted by enitharmon on Thu, 07/24/2008 - 23:37.
This may be a silly question and it may not belong in this forum but I'll ask anyway.
Sometimes, on a fine evening, I treat myself to haddock and chips and take it to my local beach to eat it and then sit and watch the sun go down over the Irish Sea. I idle the time away by lobbing pebbles down the beach and watching how they behave when they land.
Sometimes they just land. Their energy is absorbed and they remain more or less where they fell. This doesn't surprise me. Sometimes they land on another pebble in such a way that they bounce off in a random direction. This doesn't surprise me either. But sometimes they strike another pebble in such a way that they fly off with apparently sharply increased energy and angular momentum, sometimes even travelling quite considerable distances in several skips. Occasionally, such a pebble has been observed flying high over my head to land behind me, so clearly it has acquired more energy than I imparted to it when I lobbed it. But both energy and angular moment are supposed to be conserved, and the other pebbles on the beach aren't moving. So, my question is, what is going on here?
GeologyRocks
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Bouncing pebbles
Submitted by enitharmon on Thu, 07/24/2008 - 23:37.This may be a silly question and it may not belong in this forum but I'll ask anyway.
Sometimes, on a fine evening, I treat myself to haddock and chips and take it to my local beach to eat it and then sit and watch the sun go down over the Irish Sea. I idle the time away by lobbing pebbles down the beach and watching how they behave when they land.
Sometimes they just land. Their energy is absorbed and they remain more or less where they fell. This doesn't surprise me. Sometimes they land on another pebble in such a way that they bounce off in a random direction. This doesn't surprise me either. But sometimes they strike another pebble in such a way that they fly off with apparently sharply increased energy and angular momentum, sometimes even travelling quite considerable distances in several skips. Occasionally, such a pebble has been observed flying high over my head to land behind me, so clearly it has acquired more energy than I imparted to it when I lobbed it. But both energy and angular moment are supposed to be conserved, and the other pebbles on the beach aren't moving. So, my question is, what is going on here?
Rosie
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