A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2019 Jan 27, 03:16 -0800
Bill. How about this?
If the centre of gravity of a fast spinning gyro becomes out of line with the gyro’s spin axis, gravity doesn’t cause the gyro to topple further or swing back into line as might be expected from either a top heavy or bottom heavy gyro. Instead, the gyro precesses like a child’s spinning top such that its spin axis follows a path akin to moving around the outer surface of a cone with the apex of the cone coinciding with pivot point of the gyro. This conical movement awakens fresh forces upon the gyro. Typically, the pivot will attempt to follow a circular path of small radius, as opposed to the zero radius of a perfectly upright spin axis. Therefore, there will be a tiny frictional force in the opposite direction to the one in which the pivot is trying not very successfully to walk. This is akin to pulling at the bottom of the spin axis, and due to the same process which causes a spinning gyro to move off in a counterintuitive direction when disturbed will cause the gyro to gradually re-erect itself.
Note for spin and seam bowlers. The similarities between the spin grooves on the gyro and the seam of a cricket ball, the differences in roughness between the upper and lower surfaces of the gyro, and the effect of these and of the gyro’s wobble in the disturbed air inside the gyro casing should not be overlooked. DaveP