On 27/7/2007 5:02 AM, Michel Jullian wrote: Thanks for the comments.
Harry, a few comments in your text below: "Consider a wheel located on Earth's equator (see fig. below). Initially a brake prevents the wheel from turning so the wheel is not turning relative to the ground. Next the brake is released and assuming the axel [axle] of the wheel is frictionless and since the Earth is slowly turning the wheel will begin [continue] to slowly turn about its own centre at the same rate as the Earth's rotation. "continue" is consistent with the account you give below. For someone standing beside the wheel it might appear as if the brake were still applied. However, if the wheel is turning about its own centre the periphery of the wheel is subject to an associated centrifugal force. The person beside the wheel would deny this unless they knew the brake was released." [no, the centrifugal force is a fictitious force associated to the motion of the non-inertial frame of reference (here the ground-bound frame, or that bound to the bottom of the wheel, which is the same) wrt to an inertial frame of reference (here the Earth center+distant stars frame). This motion, whichever way you look at it, is a simple rotation at 1 turn per day around the Earth axis, at one Earth radius distance] Pointing out that it is a "fictitious" force does not invalidate what I am saying. Of course the hub of the wheel continues to rotate about the Earth's axis of rotation. However, please entertain my assertion as a testable conjecture. If the wheel with the brake off is really rotating about its own centre then the tension in the spokes should differ from the tension in the spokes when the brake on. Harry
