# How is it possible for the earth to rotate at different speeds at different latitudes? **URL:** \ **Category:** Factual Questions\ **Created:** [September 19, 2014, 2:52pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932 "2014-09-19T14:52:15Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![davidmich](https://avatars.discourse-cdn.com/v4/letter/d/e56c9b/32.png) [@davidmich](https://boards.straightdope.com/u/davidmich)\ **Post date:** [September 19, 2014, 2:52pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/1 "2014-09-19T14:52:15Z")
Hi How is it possible for the earth to rotate at different speeds at different latitudes? So, for example the earth rotates at 1,700 km/h at the equator, but at slower speeds in upper and lower latitudes, and slowest of all at the poles. I look forward to your feedback. davidmich ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [September 19, 2014, 2:55pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/2 "2014-09-19T14:55:35Z")
It isn’t rotating at a different rate. The points on the surface of the earth are moving at different speed because of the different radius of a circular cross section at different latitudes. Rotation is measured in units like RPM, not the speed of different points on the rotating object. ---
**Author:** ![Flywheel](https://avatars.discourse-cdn.com/v4/letter/f/eb8c5e/32.png) [@Flywheel](https://boards.straightdope.com/u/Flywheel)\ **Post date:** [September 19, 2014, 3:03pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/3 "2014-09-19T15:03:38Z")
[Obligatory Calvin & Hobbes link.](http://assets.amuniversal.com/d73efdd0dece013171ac005056a9545d) ---
**Author:** ![Canadjun](https://avatars.discourse-cdn.com/v4/letter/c/76d3ee/32.png) [@Canadjun](https://boards.straightdope.com/u/Canadjun)\ **Post date:** [September 19, 2014, 3:12pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/4 "2014-09-19T15:12:41Z")
Spin a globe and think about the distance any point on the globe covers in one rotation. ---
**Author:** ![The\_Second\_Stone](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@The\_Second\_Stone](https://boards.straightdope.com/u/The_Second_Stone)\ **Post date:** [September 19, 2014, 4:12pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/5 "2014-09-19T16:12:45Z")
Imagine you are at the South Pole. You walk 100 yards away from the pole. You stand there all day and make one revolution around the world! You’ve traveled about 314.15 yards in a 24 hour period. The earth spins on it’s axis. No imagine you are standing in Lima Peru (which I am guessing is about right on the equator, if I’m wrong, stand on the equator somewhere.) You move 100 yards in any direction and stand there for 24 hours. The rotation of the axis of the earth is now going to move you the whole circumference of the earth 24,859.82 miles, roughly 1000 miles an hour. Relative to objects not on the earth. In neither case will you be inclined to the “wheeee!” ---
**Author:** ![snowthx](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snowthx/32/10660_2.png) [@snowthx](https://boards.straightdope.com/u/snowthx)\ **Post date:** [September 19, 2014, 4:38pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/6 "2014-09-19T16:38:56Z")
Next time you are a passenger in a car on the freeway, take a look at the wheels on the vehicle next to you. You should be able to just about make out the emblem at the center of the wheel, because it is going slow enough for you to see. Try to make out what brand of tire - it will be impossible since the tire is rotating much faster than the center, and you cannot see the letters. Same concept for the earth - the closer to the poles, the slower you go compared to the equator over the same time frame. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [September 19, 2014, 4:41pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/7 "2014-09-19T16:41:11Z")
How would it be possible for it NOT to do that? ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [September 19, 2014, 4:42pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/8 "2014-09-19T16:42:04Z")
> [@Flywheel](#): > > [Obligatory Calvin & Hobbes link.](http://assets.amuniversal.com/d73efdd0dece013171ac005056a9545d) This is the best answer; both in content, and in presentation. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [September 19, 2014, 5:25pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/9 "2014-09-19T17:25:17Z")
> [@Johnny\_L.A](#): > > This is the best answer; both in content, and in presentation. I agree. I wish I’d thought of it and saved myself some typing. ---
**Author:** ![chrisk](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@chrisk](https://boards.straightdope.com/u/chrisk)\ **Post date:** [September 19, 2014, 5:38pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/10 "2014-09-19T17:38:09Z")
Because that’s how rotation works. Why would you think it was impossible? 😉 ---
**Author:** ![DrCube](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@DrCube](https://boards.straightdope.com/u/DrCube)\ **Post date:** [September 19, 2014, 6:21pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/11 "2014-09-19T18:21:40Z")
> [@Canadjun](#): > > Spin a globe and think about the distance any point on the globe covers in one rotation. For that matter, spin anything. OP have you ever actually spinned anything? A top, a record, a tire, yourself? ---
**Author:** ![jrepka](https://avatars.discourse-cdn.com/v4/letter/j/ee59a6/32.png) [@jrepka](https://boards.straightdope.com/u/jrepka)\ **Post date:** [September 19, 2014, 6:52pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/12 "2014-09-19T18:52:00Z")
All locations on the Earth rotate at the same _**[Angular Velocity](http://en.wikipedia.org/wiki/Angular_velocity)**_. Different latitudes, since they lie on the circumference of circles of different radii, rotate at different _**[speeds](http://en.wikipedia.org/wiki/Speed)**_. ---
**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:** [September 19, 2014, 7:27pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/13 "2014-09-19T19:27:23Z")
For a solid object that is spinning on an fixed axis, we can talk about **angular speed** and **tangential speed**. If the **angular speed** is constant (e.g. the object rotates 20 degrees per second around a fixed axis), the speed of any atom or molecule in the object (in meters per second) will be a function of the shortest distance between the atom/molecule and the axis the object is spinning around. In other words, the radius. The farther an atom/molecule is from the axis, the faster it will be moving. We call this speed the **tangential speed** for a given location (or atom/molecule) on or in the object. ---
**Author:** ![davidm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidm/32/225_2.png) [@davidm](https://boards.straightdope.com/u/davidm)\ **Post date:** [September 19, 2014, 7:38pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/14 "2014-09-19T19:38:16Z")
So if the disk is big enough, the outer edge could be traveling faster than light. :eek: Not really, of course. The motor would need an infinite amount of energy to do that. But that brings a thought to mind. Does the outer edge of the spinning record age slower than the center? It’s going faster, plus the acceleration is greater (I think). ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [September 19, 2014, 7:49pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/15 "2014-09-19T19:49:17Z")
> [@davidm](#): > > So if the disk is big enough, the outer edge could be traveling faster than light. :eek: Nope - unless ofcourse you have infinite energy to spin it. On the other hand, if you were to take a laser pointer- shine it on the moon and spin it fast enough, the spot on the moon can move faster than the speed of light :p- and it does not violate relativity. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [September 19, 2014, 7:49pm UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/16 "2014-09-19T19:49:53Z")
> [@davidm](#): > > So if the disk is big enough, the outer edge could be traveling faster than light. :eek: > > Not really, of course. The motor would need an infinite amount of energy to do that. > > But that brings a thought to mind. Does the outer edge of the spinning record age slower than the center? It’s going faster, plus the acceleration is greater (I think). There’s something about a large [spinning cylinder](http://en.wikipedia.org/wiki/Tipler_cylinder)that would allow time travel. And I think there are threads about the aging thing. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [September 20, 2014, 12:02am UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/17 "2014-09-20T00:02:03Z")
If you mean precisely, if carried out to many decimal places, there is a difference in angular velocity at different latitudes. Which is why we have tides, which are, after all, on the surface of the earth. Maybe even continental drift is a form of one part of the surface rotating at a different speed than another. As I recall, the bands on Jupiter rotate at a slightly different angular velocity from each other. I’m not sure if we know whether the fluid under the earth’s crust rotates at a constant angular velocity at all latitudes. ---
**Author:** ![D18](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@D18](https://boards.straightdope.com/u/D18)\ **Post date:** [September 20, 2014, 12:14am UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/18 "2014-09-20T00:14:38Z")
Now that you have your head around that concept, do a search of the boards and you’ll learn two fascinating outcomes of this: things weigh less at the equator than at increasing/decreasing latitudes (at a scale measurable by, well, a household scale) and North/South rivers (in the Northern hemisphere; vice versa in the Southern) flow uphill relative to the centre of the earth. Both of those fun facts I learned right here in GQ! ---
**Author:** ![Oddball\_92](https://avatars.discourse-cdn.com/v4/letter/o/b3f665/32.png) [@Oddball\_92](https://boards.straightdope.com/u/Oddball_92)\ **Post date:** [September 20, 2014, 12:37am UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/19 "2014-09-20T00:37:34Z")
I would liken it to a ceiling fan. The outside end of the blade makes a complete revolution at precisely the same time as the inside end of the blade, but the outside of the blade has to travel a much longer distance than the inside end. Therefore the outside end of the blade travels much faster. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [September 20, 2014, 12:56am UTC](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932/20 "2014-09-20T00:56:50Z")
> [@davidm](#): > > But that brings a thought to mind. Does the outer edge of the spinning record age slower than the center? It’s going faster, plus the acceleration is greater (I think). Somewhere over the years, I read an explanation of Relativity that touched on exactly this point. Yes, the outer edge of a record ages more slowly than the inner-most track, and the amount of this difference is computable and measurable. It was some figure on the order of a small number of billionths of a second (per revolution, I take it). [Next page](https://boards.straightdope.com/t/how-is-it-possible-for-the-earth-to-rotate-at-different-speeds-at-different-latitudes/698932.md?page=2)