In reply to Harry Veeder's message of Mon, 1 Aug 2011 19:22:34 -0700 (PDT): Hi, [snip] >This reminds me of a pre 17th century argument that the Earth cannot be >turning. >As everyone knows if the Earth was turning then the ground would move away >from you whenever you jumped in the air. However from our experience we know >it does not, theorefore the Earth is not turning.
Actually the old argument is correct, in concept, but wrong in magnitude. In order to come down in exactly the same spot (assuming a perfectly vertical jump), one would have to maintain the same angular velocity (degrees of arc / second) in the air that one had on the ground (and, due to the larger radius, travel a larger distance at a higher linear velocity parallel to the surface). Since one's linear velocity is not going to increase (conservation laws), one always comes down a tiny distance West of where one started. Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
