(published on 10/22/2007)
No, the Earth has gravity just because it has mass. It would have almost exactly the same gravity even if it wasn't spinning at all. The gravitational effects of its spin are extremely subtle, and have not yet been reliably measured.
[update: The tiny spin effect, "frame dragging", has finally been accurately measured, in an extremely difficult satellite experiment.]
If you get a chance, we'd love to hear how the spin-gravity connection came to mind.
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Mitch- The short answer is that we (at least those of us doing the answering here) don't know. Tom discusses some of what's known above.
(published on 06/12/2013)
Gravity comes from all forms of energy/momentum. The Higgs field contributes the rest mass (rest energy) of the massive elementary particles of ordinary matter (electrons, quarks) , so it plays a big role in familiar gravity. Other terms in the mass of composite particles (protons, neutrons, nuclei) come from the interactions between the more elementary ones. Since the type of bound states the more elementary ones form depends on their masses, and hence on the Higgs contribution, it's important for all ordinary gravity. Gravity would exist without it, however.
(published on 09/25/2014)
I think you have your numbers wrong. According to the latest measurements the mass of Mercury is only about one twentieth that of the earth. Its density is about the same as the earth's.
Check the latest NASA numbers:
328.5E21 kg (0.055 Earth mass)
(published on 03/31/2015)
Just to avoid confusing other readers, I'll mention that at points you use "centripetal" when you seem to mean "centrifugal".
Yes, if the Earth were spinning fast enough then its gravity would not be strong enough to hold things at the equator down and some would fly off. That effect already causes the equator to bulge a bit, so that the Earth isn't quite spherical.
A satellite in orbit isn't affected by the Earth's spin, except for a tiny, barely measurable, General Relativistic effect. The satellite stays in orbit because gravity is just strong enough to counteract the tendency to fly away in simple inertial motion. If you want to look at that in a frame rotating around with the satellite, you'd say that the centrifugal force just canceled the gravitational force.
When you jump, you do briefly become a satellite. The velocity you pick up from the Earth's rotation is much smaller than you'd need to have an orbit large enough to avoid bumping back into the Earth. It is enough, however, to help a rocket give you enough sideways velocity to get a big orbit. So it's easier to launch a satellite into an eastward-going orbit than into a westward-going one.
So you are on the right track. The one place where I think you went wrong is to think of some sort of "boundary". The net velocity is all that matters, regardless of whether it comes from the Earth's spin or from a rocket or from something else.
(published on 01/05/2016)