# earth rotation **URL:** \ **Category:** Factual Questions\ **Created:** [May 19, 2002, 3:29pm UTC](https://boards.straightdope.com/t/earth-rotation/109822 "2002-05-19T15:29:48Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![killroy](https://avatars.discourse-cdn.com/v4/letter/k/b77776/32.png) [@killroy](https://boards.straightdope.com/u/killroy)\ **Post date:** [May 19, 2002, 3:29pm UTC](https://boards.straightdope.com/t/earth-rotation/109822/1 "2002-05-19T15:29:48Z")
(1)what keeps the earth spinning? (2) is the fuel that keeps the earth fire burning below coming from the stored sun energy in plants and animals that have died . ---
**Author:** ![Wikkit](https://avatars.discourse-cdn.com/v4/letter/w/c0e974/32.png) [@Wikkit](https://boards.straightdope.com/u/Wikkit)\ **Post date:** [May 19, 2002, 4:29pm UTC](https://boards.straightdope.com/t/earth-rotation/109822/2 "2002-05-19T16:29:06Z")
(1) What would make it stop spinning? There’s no friction with space. The only thing slowing it down is the tidal force from the sun, and that’s pretty weak. Semi-related column: [What happens if the earth stops spinning?](http://www.straightdope.com/classics/a961122a.html) (2) Huh? ---
**Author:** ![rsa](https://avatars.discourse-cdn.com/v4/letter/r/839c29/32.png) [@rsa](https://boards.straightdope.com/u/rsa)\ **Post date:** [May 19, 2002, 4:40pm UTC](https://boards.straightdope.com/t/earth-rotation/109822/3 "2002-05-19T16:40:25Z")
(2) No. The “earth fire” is kept going by radioactive decay. ---
**Author:** ![drewbert](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drewbert/32/15890_2.png) [@drewbert](https://boards.straightdope.com/u/drewbert)\ **Post date:** [May 19, 2002, 5:00pm UTC](https://boards.straightdope.com/t/earth-rotation/109822/4 "2002-05-19T17:00:35Z")
1. rotational inertia. An object in motion stays in motion unless acted on by another force. As **Wikkit** said, there is no other force. Or not much, at least. 2. 3 sources of the heat inside the earth (note that it’s not “fire”, which implies a chemical process where something is burning) > [@](#): > > There are three main sources of heat in the deep earth: (1) heat from when the planet formed and accreted, which has not yet been lost; (2) frictional heating, caused by denser core material sinking to the center of the planet; and (3) heat from the decay of radioactive elements. from [http://www.sciam.com/askexpert/geology/geology7/geology7.html](http://www.sciam.com/askexpert/geology/geology7/geology7.html) ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [May 19, 2002, 6:59pm UTC](https://boards.straightdope.com/t/earth-rotation/109822/5 "2002-05-19T18:59:17Z")
> [@](#): > > \*Originally posted by Wikkit \* > [The only thing slowing it down is the tidal force from the sun, and that’s pretty weak. Not to forget the tidal effects of the moon as well. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [May 19, 2002, 8:53pm UTC](https://boards.straightdope.com/t/earth-rotation/109822/6 "2002-05-19T20:53:59Z")
> [@](#): > > \*Originally posted by bonzer \* > Not to forget the tidal effects of the moon as well. Which is a greater force than tidal effects of the sun. IIRC, Astronomers estimate that when the Earth formed, a day was about 10 to 12 hours long. ---
**Author:** ![bbeaty](https://avatars.discourse-cdn.com/v4/letter/b/c0e974/32.png) [@bbeaty](https://boards.straightdope.com/u/bbeaty)\ **Post date:** [May 19, 2002, 10:21pm UTC](https://boards.straightdope.com/t/earth-rotation/109822/7 "2002-05-19T22:21:10Z")
> [@](#): > > \*Originally posted by killroy \* > \*\*(1)what keeps the earth spinning? > > (2) is the fuel that keeps the earth fire burning below coming from the stored sun energy in plants and animals that have died . \*\* Centuries ago, religious thinkers imagined that invisible angels kept the earth spinning. But they suffered from a misconception. They assumed that all spinning objects would naturally stop… therefore, whenever an object keeps spinning, something must be doing it. Wrong! In fact, the rule is actually backwards: objects will keep spinning forever unless something stops them. The Earth is hovering in space, so there’s little to slow it down. Today we think when the Earth formed, the incoming rocks weren’t just moving inwards. Instead they spiralled inwards, so they made the big blobby Earth spin as well. As for #2, if it was decaying plants keeping things warm, then the hottest part would be just under the ground. We know that the center of the Earth is far hotter than the surface (the iron core is molten, except for the very center.) Back around 1900 geologists thought that the Earth had been red hot when it first formed, and that it was cooling ever since. Decades later they found that this couldn’t be right, because the Earth is so old that the whole thing should have cooled off long ago. Today we know that the slight radioactivity of the rocks is generating heat. The heat has to travel through thousands of miles of rock before it can escape. Just a tiny, continuous amount of radioactive heating is enough to keep the center of the Earth red hot. (If the Sun suddenly went dark, the Earth’s surface wouldn’t cool to absolute zero. If I recall, I think it would hover around 10F on average.) ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [May 20, 2002, 3:50am UTC](https://boards.straightdope.com/t/earth-rotation/109822/8 "2002-05-20T03:50:21Z")
So is the iron core spinning at exactly the same rate as the crust? Do the tidal forces affect one or the other more? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 20, 2002, 4:35am UTC](https://boards.straightdope.com/t/earth-rotation/109822/9 "2002-05-20T04:35:31Z")
The liquid parts are not moving uniformly, and in fact aren’t even simply rotating. The motion of the core is mostly what causes the magnetic field of the planet. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [May 20, 2002, 9:49am UTC](https://boards.straightdope.com/t/earth-rotation/109822/10 "2002-05-20T09:49:45Z")
> [@](#): > > \*Originally posted by bbeaty \* > **Back around 1900 geologists thought that the Earth had been red hot when it first formed, and that it was cooling ever since. Decades later they found that this couldn’t be right, because the Earth is so old that the whole thing should have cooled off long ago. Today we know that the slight radioactivity of the rocks is generating heat. The heat has to travel through thousands of miles of rock before it can escape. Just a tiny, continuous amount of radioactive heating is enough to keep the center of the Earth red hot.** No. The geologists thought that the Earth was old, based upon their studies and observed rates, but Kelvin estimated that the Earth couldn’t be that old–because of the high rate of heat loss at the surface. It would have cooled completely in a few million years. It turned out that radioactive elements are concentrated in the crust, and the heat loss from the interior is not as high as Kelvin thought it was. But most of the radioactive heating is near the surface. Most of the deep internal heat is from energy left over from the formation of the Earth. There is some energy released as the inner core grows, also–I’m not sure why that [Sciam link](http://www.sciam.com/askexpert/geology/geology7/geology7.html) doesn’t mention that, it’s different from the frictional heating.