That makes practical sense, although approximations can sometimes result in models that deviate significantly from reality. Remember when I used a simplified mathematical model of a pendulum to design a perpetual motion machine?
Harry On Sat, Dec 3, 2016 at 6:28 PM, Stephen A. Lawrence <sa...@pobox.com> wrote: > Re: Lighter materials migrating to where the gravity is lower: It doesn't > work that way. A pingpong ball on the surface has no way of knowing that > 1000 miles down it would be lighter. > > What migrates up, and what migrates down, depends only on the local > gravitational field, and the relative densities of the items in question. > Locally, over the regions where convection is actually sorting things out, > the strength of gravity can be considered to be constant. > > Convection, just like the buoyancy force, is due to differential pressure > on the bottom and top of an object. When we're dealing with tiny objects, > the differential pressure is due essentially entirely to the density of > other "stuff" around the object, which results in increasing pressure with > depth. Again, on the scales which are relevant to sorting molecules, fine > particles, tiny bubbles, etc, gravity can be treated as constant. > > > On 12/03/2016 11:21 AM, H LV wrote: > > > Q: why don't lighter elements find there way to the centre of the Earth if > gravity is lowest at the centre? > > Harry > > > New study indicates Earth's inner core was formed 1 - 1.5 billion years ago > October 7, 2015 > http://phys.org/news/2015-10-earth-core-billion-years.html > > On Sat, Dec 3, 2016 at 10:47 AM, H LV <hveeder...@gmail.com> wrote: > >> Possible generation of heat from nuclear fusion in Earth’s inner core >> >> http://www.nature.com/articles/srep37740 >> >> <<The cause and source of the heat released from Earth’s interior have >> not yet been determined. Some research groups have proposed that the heat >> is supplied by radioactive decay or by a nuclear georeactor. Here we >> postulate that the generation of heat is the result of three-body nuclear >> fusion of deuterons confined in hexagonal FeDx core-centre crystals>> >> >> Harry >> > > >
