polhode การใช้

• The herpolhode is generally an open curve, which means that the rotation does not perfectly repeat, but the polhode is a closed curve.
• Poinsot s geometric interpretation of Earth s polhode motion was still based on the incorrect assumption that the Earth was a completely rigid rotating body.
• This meant that a simple time-average polhode model was insufficient, and a detailed orbit by orbit model was needed to remove the effect.
• See Poinsot's construction, which is summarized by the delightful phrase " the polhode rolls without slipping on the herpolhode lying in the invariable plane ".
• The rigid part of the Earth s mass is not symmetrically distributed, and this is what causes the Chandler Wobble, or more precisely, the Earth s polhode path.
• With the electrostatic torque modeled as a function of axis misalignment, and the polhode motion modeled at a sufficiently fine level, it was hoped to isolate the relativity torques to the originally expected resolution.
• It was not until 1891 that the American astronomer, Seth Carlo Chandler, made measurements showing that there was a periodic motion of 14 months in the Earth s wobble and suggesting that this was the polhode motion.
• If energy is dissipated while an object is rotating, this will cause the polhode motion about the axis of maximum inertia ( also called the "'major principal axis "') to closing in on the axis.
• The path traced out on this ellipsoid by the angular velocity vector \ boldsymbol \ omega is called the "'polhode "'( coined by Poinsot from Greek roots for " pole path " ) and is generally circular or taco-shaped.
• Although electrostatic patches caused by non-uniform coating of the spheres were anticipated, and were thought to have been controlled for before the experiment, it was subsequently found that the final layer of the coating on the spheres defined two halves of slightly different polhode motion by inducing currents in the housing electrodes, causing the motion to change with time.
• Rotation about the axis of minimum inertia ( also called the "'minor principal axis "') is also stable, but given enough time, any perturbations due to energy dissipation or torques would cause the polhode path to expand, in larger and larger ellipses or circles, and eventually migrate through the separatrix and its axis of intermediate inertia to its axis of maximum inertia.