<p>The Earth <strong>does</strong> spin like an unbalanced top. The Earth's rotation axis is not fixed. It instead moves in a complex manner due to a combination of external torques exerted by the Moon and Sun, a torque-free nutation due to the oblate shape of the Earth, and also due to changes on and in the Earth.</p>
<p>The torque-induced motions are called precession and nutation, distinguished by period. The largest and slowest of these motions is the axial precession. This causes the Earth's rotation axis to trace out a cone over the course of 26000 years.</p>
<p><a href="https://i.sstatic.net/GYtyX.gif" rel="nofollow noreferrer"><img src="https://i.sstatic.net/GYtyX.gif" alt="" /></a><br />
<sub>(source: <a href="https://solarsystem.nasa.gov/basics/bsf16-9.gif" rel="nofollow noreferrer">nasa.gov</a>)</sub></p>
<p>The torque-induced nutations are also cyclical motions induced by the Moon and the Sun. These are much smaller in magnitude and have a much shorter period. The largest of these has a magnitude of about 20 arc seconds and a period of 18.6 years. All other nutation terms have much smaller magnitude and have shorter period.</p>
<p>The torque-free nutation would have a period of about 305 days if the Earth was solid. The oceans, the atmosphere, and the outer core alter this. The Chandler wobble has a period of about 433 days and a magnitude of less than an arc second. Because the Chandler wobble isn't as predictable as are precession and nutation, it's lumped into a catch-all category called &quot;polar motion.&quot; The redistribution of water over the course of a year (e.g., snow on Siberia in the winter but not in the summer) results in a yearly component of the polar motion.</p>
<p>There are lots and lots of other factors, all small. Polar motion is observed after the fact.</p>

CC BY-SA 3.0
2016-05-16T21:17:00.247Z
How the Japan Earthquake Shortened Days on Earth: http://www.space.com/11115-japan-earthquake-shortened-earth-days.html "analysis of the 8.9-magnitude earthquake in Japan has found that the intense temblor has accelerated Earth's spin, shortening the length of the 24-hour day by 1.8 microseconds"
Wayfaring Stranger
CC BY-SA 3.0
2016-05-16T21:53:55.403Z
@WayfaringStranger - That is a calculated result. The noise in the measurements are orders of magnitude higher than that.
David Hammen
CC BY-SA 4.0
2016-05-16T20:34:21.320Z
2019-02-19T20:48:09.470Z
2020-06-17T09:47:40.653Z
David Hammen
<p>If put enough weight on a particular point on Earth's surface disturbing the balance between hemispheres, is it possible that the Earth's spin could change like an unbalanced spinning top?</p>

CC BY-SA 3.0
2016-05-16T21:28:07.640Z
Answered here: http://physics.stackexchange.com/questions/156744/changing-earth-angle-of-revolution
called2voyage
CC BY-SA 3.0
2016-05-17T07:37:25.327Z
By the way I think this is on topic here in Astronomy too, because true polar wander has been studied (modelled) on, for example, Io.
Andy
CC BY-SA 3.0
2016-05-17T14:12:59.120Z
@Andy This has been addressed early on in the community. Just because a question is applicable to other worlds doesn't mean asking that question about Earth is on topic, unless the question is broadened to include other worlds as well.
called2voyage
CC BY-SA 3.0
2016-05-17T14:14:27.917Z
@Andy The reason for that is that early on on this site we received a relatively large volume of questions about Earth that drew attention away from more astronomy-focused questions.
called2voyage
CC BY-SA 3.0
2016-05-17T14:39:27.997Z
@called2voyage thanks, understood. I was confused by the blurb above "unless directly related to phenomena observable on other celestials", but of course that would mean most of Geology would become astronomy :)  But I get it now.
Andy
<earth><amateur-observing><fundamental-astronomy>
Does weight influence Earth's spin?
Umer
# Does weight influence Earth's spin?

(Asked by: username_0 on 2016-05-16)

If put enough weight on a particular point on Earth's surface disturbing the balance between hemispheres, is it possible that the Earth's spin could change like an unbalanced spinning top?

**Tags:** earth, amateur-observing, fundamental-astronomy

> **Comments:**
> **username_1**: Answered here: http://physics.stackexchange.com/questions/156744/changing-earth-angle-of-revolution  
> **username_2**: By the way I think this is on topic here in Astronomy too, because true polar wander has been studied (modelled) on, for example, Io.  
> **username_1**: @username_2 This has been addressed early on in the community. Just because a question is applicable to other worlds doesn't mean asking that question about Earth is on topic, unless the question is broadened to include other worlds as well.  
> **username_1**: @username_2 The reason for that is that early on on this site we received a relatively large volume of questions about Earth that drew attention away from more astronomy-focused questions.  
> **username_2**: @username_1 thanks, understood. I was confused by the blurb above "unless directly related to phenomena observable on other celestials", but of course that would mean most of Geology would become astronomy :)  But I get it now.  

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## 1 answers

### Answer by username_3 on 2016-05-16. Score: 3 | Accepted answer

The Earth **does** spin like an unbalanced top. The Earth's rotation axis is not fixed. It instead moves in a complex manner due to a combination of external torques exerted by the Moon and Sun, a torque-free nutation due to the oblate shape of the Earth, and also due to changes on and in the Earth.

The torque-induced motions are called precession and nutation, distinguished by period. The largest and slowest of these motions is the axial precession. This causes the Earth's rotation axis to trace out a cone over the course of 26000 years.

[![](https://i.sstatic.net/GYtyX.gif)](https://i.sstatic.net/GYtyX.gif)  
(source: [nasa.gov](https://solarsystem.nasa.gov/basics/bsf16-9.gif))

The torque-induced nutations are also cyclical motions induced by the Moon and the Sun. These are much smaller in magnitude and have a much shorter period. The largest of these has a magnitude of about 20 arc seconds and a period of 18.6 years. All other nutation terms have much smaller magnitude and have shorter period.

The torque-free nutation would have a period of about 305 days if the Earth was solid. The oceans, the atmosphere, and the outer core alter this. The Chandler wobble has a period of about 433 days and a magnitude of less than an arc second. Because the Chandler wobble isn't as predictable as are precession and nutation, it's lumped into a catch-all category called "polar motion." The redistribution of water over the course of a year (e.g., snow on Siberia in the winter but not in the summer) results in a yearly component of the polar motion.

There are lots and lots of other factors, all small. Polar motion is observed after the fact.

> **Comments:**
> **username_4**: How the Japan Earthquake Shortened Days on Earth: http://www.space.com/11115-japan-earthquake-shortened-earth-days.html "analysis of the 8.9-magnitude earthquake in Japan has found that the intense temblor has accelerated Earth's spin, shortening the length of the 24-hour day by 1.8 microseconds"  
> **username_3**: @WayfaringStranger - That is a calculated result. The noise in the measurements are orders of magnitude higher than that.  

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