This is a quote from Lord Kelvin (William Thomson):“I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may be.”įollow the below link for the Planetary Spin Equations.Try to love who you are outside of your relationship. We have a concept but not enough to express it in numbers. It’s the same as saying we don’t really know how it works. “A long time ago in a galaxy far, far away.spinning gas and dust flattened into a protoplanetary disk and due conservation of angular momentum the planets are now rotating with RANDOM velocities” But nowhere in the literature can we find an accepted law of Planetary Rotation because everyone is convinced that there is nothing special about the rotation of the planets. Equations are derived from these laws and hence the birth of Celestial Mechanics. Newton’s Law of universal gravitation and Kepler’s Law of planetary motion describes the movement of planets around the sun. Later other planets form from other over-dense bands of the disk. Once the planet has formed and any remaining moons have bound themselves the planet, the ring no longer exists, leaving a planet and its moons if any in a stable orbit around the sun. Moons are remaining large particles in the ring distant from the planet. This effect converts spin of the ring to spin of mutually bound particles within the ring.įinally the ring collapses to one remaining particle which is the planet hatched by the ring. The angular momentum of the ring increases as particles falling against the direction of spin of the ring fall inward from the circumference while the particles falling with the direction of spin fall outwards, so that mutual gravitational attraction of particles causes them to orbit one another rather than collide. Ring particles collide and the average particle size increases while the number of particles decreases. The ring thus migrates inwards from the disk to the sun. The ring particles fall towards each other around the ring, and such attractions cause the ring to contract its circumference. A ring forms from a disk over-density band, reducing to a nominally 1d ring from a 2d band. The disk flattens from a 3d cloud to a 2d disk. So it could be described as this axial rotation of planets resulting in conservation of the angular momentum of the materials in the protoplanetary disk, forming during the accretion period of the planetary system as the protoplanets gain in weight, and preserve this angular momentum due to inertia of their radial velocity. Source: Scientific American article on Why and how do planets rotate? (George Spagna) Similarly, her rotation slows when she extends her arms at the
Of rotation, her speed increases and her angular momentum remains the One nice description for this angular momentum preservation, and why the planets appear to rotate faster than their surrounding protoplanetary disk goes like this:Ĭonservation of angular momentum explains why an ice skater spins more Generated image (virtual fly-by) from a simulation of the accretion period of the protoplanetary disk, showing preservation ofĪngular momentum in the orbit around a Jupiter-size planet, as it clears its neighborhood. As the planets evolve during their protoplanetary stage and accrete materials from the protoplanetary disks, which are gravitationally collapsing interstellar dust and gases, these accreted particles retain some of the angular momentum from the materials they form from and being in constant motion.
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