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Q & A: What keeps the earth spinning?

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Most recent answer: 08/31/2015
Q:
where does the torque needed to spin the earth come from?How has this spinning sustained?Please reflect in the light of law of conservation of energy.
- rajiv sakalkale (age 48)
nagpur,india
A:

Hi Rajiv,

Let me turn your question around: what torque on the earth would possibly slow it down? The earth started spinning during its formation, and that angular momentum doesn't have anywhere to go.

Gravity doesn't exert a torque, and the asteroids that hit the earth only change its rotation infinitesimally. Actually, I'm sure the object which crashed into the earth and created the moon changed the earth's angular rotation, but since then it has been constant.

Angular momentum is conserved, and here the energy that goes with it is conserved too, so the earth spins happily on and on.

David Schmid


(published on 05/30/2013)

Follow-Up #1: conservation of angular momentum

Q:
I think there is a deeper reason for what keeps the earth spinning. Considering that I haven't ever heard of either a planet not spinning, or a sun not spinning, or a galaxy not spinning, I don't see any evidence that anything actually ever stops spinning. Has astronomy ever discovered a planet sized object which wasn't spinning? If you know of one, please let me know!Angular momentum it seems would be conserved in a rotating body if that body were solid throughout. However, we know that the earth is molten, like the sun. Therefore it's logical to think that there are huge frictional forces consuming the energy of rotation through friction and generating heat. If this is the case, it would seem that spinning planets would slow down pretty fast. Although I don't have any kind of calculation for that, it seems intuitive. Yet, again, there is no evidence that I am aware of in which a Sun has stopped spinning.Entire galaxies continue to spin - with huge frictional forces on grand gravitaional scales. Where does to rotational energy come from in the first place - all those spinning atoms/protons/electrons etc... - what keeps them spinning? Even if the idea that conservation of angular momentum was to generate the rotation of a solar system during its formation, it still doesn't account for the initial energy that got all those quadrillions of atoms to spin in the first place. What's the source of energy for the so-called "big bang"? I don't buy that theory until a source of energy for the event is discovered.I would propose an investigation into some of the ideas of modern or even un-proven physics theories which talk about infinite potentials and/or energy density of the vacuum. What if, as Haramein proposed, Spin is an intrinsic result of the gravitation of an object - that the gravity not only curves the space around it (the proven theory of Einstein) - but curls the space around it so that the spin is generated and perpetuated by the vacuum itself, that source which feeds a planet it's own gravitational force (it would seem).After all, gravity is a force. And it would seem that a force would require a source of energy to maintain that force. Likewise with magnetism. Two permanent magnets attracting each other seems like nothing new. But where does that constant force of attraction come from? If we want to make an electromagnet - which intereacts with permanent magnetic fields - we have to supply a coil with a constant source of energy - meaning we plug it into the wall, or a generator of some sort. So where does the energy come from which supplies these forces of gravity or natural magnetism to act on a constant basis???We normally say that gravity is the force that pulls us downward. What if it's a force that's pushing us towards the earth - like a river of energy flowing towards the center of the earth - and we are caught in it. Better yet, a whirlpool of energy, and the earth is spinning in it. Perhaps the presence of matter in space draws energy towards it from the infinite potential of the vacuum, and as that energy flows towards the object, it flows in a spiral - just like all the natural phenomenon of hurricanes and tornados etc... - and that spiralling energy causes the rotation of the object. Where does all that energy go??? into the object, heating it up through the internal friction of the molten core? Or perhaps ejected out the top or bottom as in a huge quasar?Of course I don't know. I'm just looking for answers that make sense.
- Ocean (age 39)
Cottonwood, CA, USA
A:

There's a mistake at the core of your question. Energy and angular momentum are two very different things with separate conservation laws. Yes, a fluid sphere with parts that are spinning at different rates will lose some rotational kinetic energy to heat via friction as the parts come to spin at the same rate. The total angular momentum won't change as some parts speed up and others slow down. So there's no mystery to begin with.

The arguments about vortices and space and so on were the type of thing that some ancient Greeks wondered about in the very earliest phases of scientific speculation. That's all been replaced with real quantitative theories that work very well.

Mike W.


(published on 08/31/2015)

Follow-up on this answer.