# If the earth stopped spinning.... **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [August 15, 2001, 10:50pm UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459 "2001-08-15T22:50:21Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [August 21, 2001, 7:44pm UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/21 "2001-08-21T19:44:01Z")
> [@](#): > > \*Originally posted by Chronos \* > \*\*Of course, anyone in orbit at the time would have no problem. \*\* So nothing would happen to the Moon? I should have realized that. ---
**Author:** ![ss138](https://avatars.discourse-cdn.com/v4/letter/s/a88e57/32.png) [@ss138](https://boards.straightdope.com/u/ss138)\ **Post date:** [August 22, 2001, 2:55am UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/22 "2001-08-22T02:55:46Z")
So if everything on earth is spinning around about 1000mph, would it be safe to assume that we have a certain amount of centrifical force acting on us? This centrifical force would be pushing on us in an upward motion countering the effects of gravity. Therefore we would weigh more if the earth stopped spinning. How much more would we weigh? ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [August 22, 2001, 3:49am UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/23 "2001-08-22T03:49:29Z")
Did you read Cecil’s column? **bibliophage** linked to it near the top of this thread. Your question is exactly what Cecil was answering; what everyone has been talking about here is the tangent. Quoth Cecil: > [@](#): > > How much more would you weigh? Well, figuring in your newtons, your velocity, and your gravitational constant . . . about five ounces for a hundred-pound person. > > At the equator. ---
**Author:** ![ss138](https://avatars.discourse-cdn.com/v4/letter/s/a88e57/32.png) [@ss138](https://boards.straightdope.com/u/ss138)\ **Post date:** [August 22, 2001, 4:32am UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/24 "2001-08-22T04:32:17Z")
Thanks Achernar, I’ll be sure to read all the posts and links next time. One other, thing can we qustion Cecil’s conclusions or make our own? I’m not much in the physics and mathmatics depatment but what kind of an equation gives him 5ozs. per 100lbs.? What is the formula for finding the amount of centrifical force? ---
**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:** [August 22, 2001, 7:01pm UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/25 "2001-08-22T19:01:15Z")
The acceleration due to gravity is approximately 9.8 meters per second squared at the surface of the Earth. The simplest formula for centrifugal acceleration is a[sub]c[/sub] = v[sup]2[/sup]/r , where v is the speed of the object, and r is the radius of rotation. To get a force out of either of these accelerations, you multiply by the mass of the object. I don’t have time to check the numbers myself right now, but I’m pretty sure that if Cecil hadn’t gotten it right, one of us nerds would have noticed by now. ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [August 22, 2001, 8:49pm UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/26 "2001-08-22T20:49:19Z")
I’m re-considering the Moon in this scenario: If the Earth were to stop rotating for whatever reason, the Moon would still orbit the Earth. But wouldn’t tidal drag from the Moon’s gravity cause the Earth to start rotating again (albeit slowly)? And wouldn’t the loss of momentum cause the Moon to spiral away from the Earth? ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [August 22, 2001, 9:43pm UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/27 "2001-08-22T21:43:27Z")
**ss138** , here’s how you do it: You could use **Chronos** ’s value for the surface acceleration of the Earth and make things easier, but since Cecil mentioned the Gravitational Constant, I think we’d better do the same. The force of attraction between two bodies is: F[sub]G[/sub] = GMm/R[sup]2[/sup] where G is the Gravitational Constant, M is the mass of the Earth (in this case), m is the mass of the person, and R is the Earth’s radius. In this case. We also have a force pushing up - that’s the centrifugal force. Its magnitude is: F[sub]C[/sub] = mv[sup]2[/sup]/R where v is the velocity of the person. We can do better than this, though. v = 2_pi_×R/T where T is the period of rotation, that is, one day. Additionally, we are given: F[sub]G[/sub] - F[sub]C[/sub] = 100 lbs Solving for F[sub]C[/sub]: F[sub]C[/sub] = 100 lbs × (GMT[sup]2[/sup]/4_pi_[sup]2[/sup]R[sup]3[/sup] - 1)[sup]-1[/sup] Finally, we know: G = 6.67259×10[sup]-11[/sup] m[sup]3[/sup]/kg·s[sup]2[/sup] R = 6378 km M = 5.976×10[sup]24[/sup] kg T = 86164 s so: F[sub]C[/sub] = 0.3472 lb = 5.555 oz So, in summary, we _can_ question Cecil, but in practice, there’s never any point. ---
**Author:** ![jonfromdenver](https://avatars.discourse-cdn.com/v4/letter/j/82dd89/32.png) [@jonfromdenver](https://boards.straightdope.com/u/jonfromdenver)\ **Post date:** [August 23, 2001, 4:48am UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/28 "2001-08-23T04:48:41Z")
impressive. i don’t know what the hell it means, but it’s impressive. 🙂 ---
**Author:** ![The\_Ryan](https://avatars.discourse-cdn.com/v4/letter/t/7feea3/32.png) [@The\_Ryan](https://boards.straightdope.com/u/The_Ryan)\ **Post date:** [August 25, 2001, 2:47am UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/29 "2001-08-25T02:47:23Z")
> [@](#): > > \*Originally posted by jab1 \* > \*\*I’m re-considering the Moon in this scenario: If the Earth were to stop rotating for whatever reason, the Moon would still orbit the Earth. But wouldn’t tidal drag from the Moon’s gravity cause the Earth to start rotating again (albeit slowly)? And wouldn’t the loss of momentum cause the Moon to spiral away from the Earth? \*\* If the Earth were to stop spinning, it would see the moon orbit once every month. Currently, however, we see the moon as orbiting every day (just like the sun). So there would be **less** tidal friction than this now. Although it might point in a different direction. But that does bring up the question of which would win the tidal tug-of-war: the sun or the moon? That is, would the Earth orient itself to present the same face to the sun, or to the moon? I think that the tidal force force of a sphere is roughly proportional the angular length of the object times the density, and the sun and the moon have about the same angular length, so my guess would be the moon, since it’s so much denser. ---
**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:** [August 25, 2001, 5:13pm UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/30 "2001-08-25T17:13:38Z")
The Moon would indeed win, because the tides from the Moon are about twice as strong. This is presuming, of course, that either would win: It’s probably pretty difficult to establish a stable lock with two competing bodies of comparable tidal strength. ---
**Author:** ![Jet\_Jaguar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jet_jaguar/32/3562_2.png) [@Jet\_Jaguar](https://boards.straightdope.com/u/Jet_Jaguar)\ **Post date:** [August 25, 2001, 6:36pm UTC](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459/31 "2001-08-25T18:36:02Z")
> [@](#): > > \*Originally posted by Chronos \* > \*\*1000 MPH is (fortunately) much less than circular orbital velocity at the Earth’s surface, so the ground would not fal away at all. If it did, you’d already be in orbit, since you’re already going that fast. Don’t think a “launch”, think the mother of all car crashes. > > We’re also talking at least an order of magnitude or so greater than a bungie cord would be able to handle. I wouldn’t exactly trust water skis at that speed, either. Folks in aircraft, however, might survive, if the pilot keeps his head and is able to keep the plane aloft until the winds die down some (not sure how long that would take). Of course, anyone in orbit at the time would have no problem. The oceans and atmosphere would both continue to move, but probably not uniformly; you’d see some monster eddy currents and tsunamis, so even a good pilot might be challanged a bit. \*\* Don’t forget that velocity is dependent on your latitude, it’s 1000 mph only at the equator. The farther north/south you go, the slower your velocity. At the Arctic Circle, for example, your speed is a leisurely 200 mph. So, people in the more extreme northern or southern regions of the planet would have a better chance of survival. Excuse me while I pack my bags for Iceland… [Previous page](https://boards.straightdope.com/t/if-the-earth-stopped-spinning/76459.md?page=1)