# What makes the earth spin? **URL:** \ **Category:** Factual Questions\ **Created:** [January 9, 2001, 2:20am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097 "2001-01-09T02:20:59Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![elite](https://avatars.discourse-cdn.com/v4/letter/e/6f9a4e/32.png) [@elite](https://boards.straightdope.com/u/elite)\ **Post date:** [January 9, 2001, 2:20am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/1 "2001-01-09T02:20:59Z")
What makes the earth spin? ---
**Author:** ![Lance\_Turbo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lance_turbo/32/6156_2.png) [@Lance\_Turbo](https://boards.straightdope.com/u/Lance_Turbo)\ **Post date:** [January 9, 2001, 2:28am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/2 "2001-01-09T02:28:09Z")
Inertia. ---
**Author:** ![Dr.Lao](https://avatars.discourse-cdn.com/v4/letter/d/2bfe46/32.png) [@Dr.Lao](https://boards.straightdope.com/u/Dr.Lao)\ **Post date:** [January 9, 2001, 2:29am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/3 "2001-01-09T02:29:48Z")
Nothing, it was spinning when we got here. The solar system formmed out of a gas cloud that was spinning very slowly. When cloud collapsed into the sun and the planets the angular momentum has got to go somewhere. Some of it caused the sun to turn on it’s axis, some caused to planets to go around the sun, and some was left over to cause the planets to rotate on their axes. ---
**Author:** ![elite](https://avatars.discourse-cdn.com/v4/letter/e/6f9a4e/32.png) [@elite](https://boards.straightdope.com/u/elite)\ **Post date:** [January 9, 2001, 2:38am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/4 "2001-01-09T02:38:00Z")
So because there is no external force to counter the rotation the earth has continued to spin and will continue to do so until acted upon by some other force. Right? ---
**Author:** ![Lance\_Turbo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lance_turbo/32/6156_2.png) [@Lance\_Turbo](https://boards.straightdope.com/u/Lance_Turbo)\ **Post date:** [January 9, 2001, 2:41am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/5 "2001-01-09T02:41:40Z")
That’s how inertia works. ---
**Author:** ![elite](https://avatars.discourse-cdn.com/v4/letter/e/6f9a4e/32.png) [@elite](https://boards.straightdope.com/u/elite)\ **Post date:** [January 9, 2001, 2:45am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/6 "2001-01-09T02:45:17Z")
Just clarifying 🙂 ---
**Author:** ![Bill\_H](https://avatars.discourse-cdn.com/v4/letter/b/a5b964/32.png) [@Bill\_H](https://boards.straightdope.com/u/Bill_H)\ **Post date:** [January 9, 2001, 5:30am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/7 "2001-01-09T05:30:45Z")
Inertia is a way of saying: “Why is it spinning? Because it’s spinning.” ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [January 9, 2001, 6:41am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/8 "2001-01-09T06:41:06Z")
> [@](#): > > So because there is no external force to counter the rotation the earth has continued to spin and will continue to do so until acted upon by some other force. Right? The earth is slowly losing energy in the form of gravity waves (think of a cork bobbing up and down in water…it slows to a stop as energy is carried away from it as waves). Of course, this energy loss is extremely small. IIRC the earth loses about enough energy to power a toaster. Not to worry though…given the size of the earth it will take MUCH longer than the life of the solar system for the earth to slow down and spiral into the sun. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [January 9, 2001, 6:44am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/9 "2001-01-09T06:44:35Z")
The rotation of the earth actually is slowing down (but very gradually) due to tidal friction. The moon is getting farther away at the same time, which makes up for the reduction of earth’s angular momentum . In the last 100 million years, the length of a day has risen from about 22 hours to 24 hours. ---
**Author:** ![Spectre\_of\_Pithecanthropus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spectre_of_pithecanthropus/32/12343_2.png) [@Spectre\_of\_Pithecanthropus](https://boards.straightdope.com/u/Spectre_of_Pithecanthropus)\ **Post date:** [January 9, 2001, 10:25pm UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/10 "2001-01-09T22:25:02Z")
> [@](#): > > \*Originally posted by bibliophage \* > \*\*The rotation of the earth actually is slowing down (but very gradually) due to tidal friction. The moon is getting farther away at the same time, which makes up for the reduction of earth’s angular momentum . In the last 100 million years, the length of a day has risen from about 22 hours to 24 hours. \*\* Very interesting. Presumably the moon must have been correspondingly closer 100 million years ago, and even closer before that. Can anyone tell us how close the moon was at that time, and how long a lunar month lasted? ---
**Author:** ![tbea925](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@tbea925](https://boards.straightdope.com/u/tbea925)\ **Post date:** [January 10, 2001, 12:25am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/11 "2001-01-10T00:25:40Z")
Love makes the world go 'round. On a billboard at a local church: “Love is the glue that holds us together”. I guess a movie about my life would be called “Glueless”. Sorry. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [January 10, 2001, 1:01am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/12 "2001-01-10T01:01:57Z")
> [@](#): > > \*Originally posted by elite \* > \*\*What makes the earth spin? \*\* What’s stopping it? Answer: nothing. Therefore, it continues to spin. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [January 10, 2001, 3:09pm UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/13 "2001-01-10T15:09:58Z")
> [@](#): > > _Javaman wrote:_ > Very interesting. Presumably the moon must have been correspondingly closer 100 million years ago, and even closer before that. Can anyone tell us how close the moon > was at that time, and how long a lunar month lasted? The info in the quote below comes from an excellent link **Mjollnir** provided in the thread about whether January 1 was always the first day of the year. The link is: [http://www.tondering.dk/claus/calendar.html](http://www.tondering.dk/claus/calendar.html) . Anything you could ever want to know about calendars seems to be in there. As to **Javaman’s** question: > [@](#): > > Our concept of a year is based on the earth’s motion around the sun. The time from one fixed point, such as a solstice or equinox, to the next is called a tropical year. Its length is currently 365.242190 days, but it varies. Around 1900 its length was 365.242196 days, and around 2100 it will be 365.242184 days. (This definition of the tropical year is not quite accurate, see section 1.1 for more details.) > > Our concept of a month is based on the moon’s motion around the earth, although this connection has been broken in the calendar commonly used now. The time from one new moon to the next is called a synodic month, and its length is currently 29.5305889 days, but it varies. Around 1900 its length was 29.5305886 days, and around 2100 it will be 29.5305891 days. > > Note that these numbers are averages. The actual length of a particular year may vary by several minutes due to the influence of the gravitational force from other planets. Similary, the time between two new moons may vary by several hours due to a number of factors, including changes in the gravitational force from the sun, and the moon’s orbital inclination. In short, there are many things affecting the orbit of the earth making the math difficult but as you can see above on average the Earth’s orbit is shortening while the Moon’s orbit is lengthening. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [January 11, 2001, 9:11am UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/14 "2001-01-11T09:11:54Z")
> [@](#): > > So because there is no external force to counter the rotation the earth has continued to spin and will continue to do so until acted upon by some other force. Right? Minor nitpick, since we’re discussing rotational motion. (Believe it or not, I’m currently teaching this topic for a physics class.) Replace “force” with “net torque” in the above statement. An object rotating about a fixed axis continues to rotate with constant angular velocity, unless it experiences a net external torque. ---
**Author:** ![Cisco](https://avatars.discourse-cdn.com/v4/letter/c/ccd318/32.png) [@Cisco](https://boards.straightdope.com/u/Cisco)\ **Post date:** [January 11, 2001, 1:06pm UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/15 "2001-01-11T13:06:41Z")
Basically we’re here because the conditions for like on this planet are just right. If the earth wasn’t spinning, the conditions for life wouldn’t be just right, therefore we wouldn’t be here and you would have asked the same question about whatever other planet we were on. ---
**Author:** ![Cisco](https://avatars.discourse-cdn.com/v4/letter/c/ccd318/32.png) [@Cisco](https://boards.straightdope.com/u/Cisco)\ **Post date:** [January 11, 2001, 1:07pm UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/16 "2001-01-11T13:07:48Z")
> [@](#): > > \*Originally posted by Cisco \* > \*\*conditions for like on this planet \*\* the conditions for **life** , of course. ---
**Author:** ![hibernicus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hibernicus/32/2802_2.png) [@hibernicus](https://boards.straightdope.com/u/hibernicus)\ **Post date:** [January 11, 2001, 1:29pm UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/17 "2001-01-11T13:29:25Z")
> [@](#): > > \*Originally posted by Jeff\_42 \* > \*\* > In short, there are many things affecting the orbit of the earth making the math difficult but as you can see above on average the Earth’s orbit is shortening while the Moon’s orbit is lengthening. \*\* I’m confused. Earlier you said “given the size of the earth it will take MUCH longer than the life of the solar system for the earth to slow down and spiral into the sun.” So, referring now to Earth’s revolution around the sun, is the earth speeding up or slowing down? Is it possible that the reason there are 0.000006 fewer days in 2000 than in 1900 is actually because of longer days (slower rotation) rather than shorter years (faster revolution)? ---
**Author:** ![Odesio](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/odesio/32/20003_2.png) [@Odesio](https://boards.straightdope.com/u/Odesio)\ **Post date:** [January 11, 2001, 1:40pm UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/18 "2001-01-11T13:40:31Z")
I have it on good authority that it is in fact love that makes the world go 'round. Marc ---
**Author:** ![Phobos](https://avatars.discourse-cdn.com/v4/letter/p/3d9bf3/32.png) [@Phobos](https://boards.straightdope.com/u/Phobos)\ **Post date:** [January 11, 2001, 1:47pm UTC](https://boards.straightdope.com/t/what-makes-the-earth-spin/49097/19 "2001-01-11T13:47:43Z")
**slowing of Earth’s rotation…** [http://itss.raytheon.com/cafe/qadir/q396.html](http://itss.raytheon.com/cafe/qadir/q396.html) “The length of the day is increasing by 0.0015 seconds every century, of which about 0.0007 seconds per century has to do with the tidal breaking of the Moon.” or [http://itss.raytheon.com/cafe/qadir/q395.html](http://itss.raytheon.com/cafe/qadir/q395.html) (with a good hyperlink to a U.S. Naval Observatory description) “The ‘24-hour’ day actually increases by 0.0014 seconds every day, per century” **moon’s receeding orbit…** [http://itss.raytheon.com/cafe/qadir/q1282.html](http://itss.raytheon.com/cafe/qadir/q1282.html) “The semi-major axis of the lunar orbit is increasing by 3.8 centimeters/year according to laser ranging measurements made since the 1970’s using the Apollo ‘corner cube reflectors’ deposited on the surface by the astronauts” **the moon’s past distance from the Earth…** [http://itss.raytheon.com/cafe/qadir/q1352.html](http://itss.raytheon.com/cafe/qadir/q1352.html) "The Moon may have been about 100 - 150,000 miles from the Earth at the outset. " (At it’s creation that is…now it is about 240,000 miles away…or 390,000 km) (And I assume the cited distance is 100,000 to 150,000 miles…not 100 miles to 150,000 miles!)