Timeline for Why doesn't the Earth accelerate towards us?
Current License: CC BY-SA 4.0
30 events
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| Nov 24, 2021 at 12:52 | history | edited | Steeven | CC BY-SA 4.0 |
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| Mar 14, 2021 at 9:03 | history | edited | Steeven | CC BY-SA 4.0 |
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| Jul 29, 2020 at 13:57 | history | edited | Steeven | CC BY-SA 4.0 |
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| Sep 18, 2019 at 19:51 | history | edited | Steeven | CC BY-SA 4.0 |
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| Jan 18, 2019 at 14:30 | vote | accept | whae | ||
| Jan 16, 2019 at 10:19 | history | edited | Steeven | CC BY-SA 4.0 |
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| Jan 16, 2019 at 8:18 | comment | added | Steeven | @Acccumulation and DavidZ, thanks for the comments. You are certainly right; I was unclear in that formulation. I have made a slight edit to not make it appear as if the pressing force on the Earth is a part of the action/reaction pair, but rather that it is equal to the weight, which is a part of the action/reaction pair. | |
| Jan 16, 2019 at 8:16 | history | edited | Steeven | CC BY-SA 4.0 |
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| Jan 16, 2019 at 7:21 | comment | added | David Z | I had posted basically the same thing @Acccumulation said and figured there's no point in repeating it - but it's true, this answer is slightly wrong about the nature of action-reaction pairs. | |
| Jan 16, 2019 at 7:14 | comment | added | Peter - Reinstate Monica | @Schwern That's depression apocalypse! | |
| Jan 15, 2019 at 23:10 | comment | added | Mark | Note that while the velocity imparted by the levitating population is trivial, the distance isn't: a hundred years is a long time, and if I haven't botched the math, the Earth will move nearly 4000 km. | |
| Jan 15, 2019 at 21:52 | comment | added | Schwern | @PeterA.Schneider But what if we used EVEN MORE?! what-if.xkcd.com/4 | |
| Jan 15, 2019 at 18:27 | comment | added | Acccumulation | ":Now there are two forces on the Earth, pushing in opposite directions. And in fact, that force called weight exactly equals the gravitational force (because those two are the action-reaction pair from Newton's 3rd law)." No, action-reaction pairs act on different bodies. The earth's gravitational force on a person and the person's gravitational force on the earth is a actin-reaction pair. The ground pushing up on a person and the person pushing down are a pair. | |
| Jan 15, 2019 at 15:55 | comment | added | Michael Richardson | @J... Wasn't there an e-mail chain about the dangers of China making each of it's citizens jump simultaneously, causing worldwide earthquakes? Nevermind. The xckd link above covers that. | |
| Jan 15, 2019 at 15:03 | comment | added | Aubreal | @PeterA.Schneider very true, as it hovers it is equivalent to standing on it; it's fun to think about when it was gaining altitude it was pushing the earth away the same way that an initial push from a jump would, and as it goes for a landing it will accelerate the earth back towards itself. The flying/hovering just delays the effects :) | |
| Jan 15, 2019 at 15:01 | comment | added | Jasper | I'd like this answer better if the parts above and below the line were swapped. | |
| Jan 15, 2019 at 14:54 | comment | added | Peter - Reinstate Monica | @J... Related: A bird or bee (or helicopter) hovering over the surface also does not exert much of a net force on the surface because it pushes the air downward which leads to higher pressure over the area which not quite accidentally pretty much cancels out the gravitational attraction. | |
| Jan 15, 2019 at 14:52 | comment | added | Peter - Reinstate Monica | @Holger That's one of the more depressing ones. (Q: What if we add more people? A: Not good.) | |
| Jan 15, 2019 at 12:16 | comment | added | J... | @AdityaBharadwaj Also consider that if you jump up from the surface of the planet you are first pushing Earth away from you. As you fall back to earth you return to each other and end up right back where you started. To effect any real delta-V you have to have some mass (or at least momentum) leaving the system. So long as we remain at the surface we can't leave the system and if we can't leave the system then we can't effect an outside acceleration on it. A spaceship to the moon, though, would effect a net acceleration as it leaves the earth completely and less of it returns than what left. | |
| Jan 15, 2019 at 11:32 | comment | added | Jonnyboy | Oh yeah, maths is hard | |
| Jan 15, 2019 at 11:30 | history | edited | Steeven | CC BY-SA 4.0 |
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| Jan 15, 2019 at 11:21 | comment | added | Jonnyboy | Just a quickie: Isn't 2.8 x 10e-3m/s roughly 30 millimetres/second? | |
| Jan 15, 2019 at 10:57 | comment | added | Holger | Reminds me on what-if.xkcd.com/8 | |
| Jan 15, 2019 at 10:31 | comment | added | Emilio Pisanty | @Aditya note also that, unless you're at the North or South poles, if you were levitating over a constant spot of the ground, then the acceleration you'd cause on the Earth would be rotating once a day, and the bulk of the contributions would cancel, as the velocity accumulated during the day would point opposite to that accumulated at night. Only the North-South component, proportional to the sine of your latitude, would survive. | |
| Jan 15, 2019 at 10:12 | history | edited | Steeven | CC BY-SA 4.0 |
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| Jan 15, 2019 at 9:53 | vote | accept | whae | ||
| Jan 18, 2019 at 14:30 | |||||
| Jan 15, 2019 at 9:43 | comment | added | Steeven | @AdityaBharadwaj Exactly. | |
| Jan 15, 2019 at 9:40 | comment | added | whae | Alright so if I am standing on the Earth's surface then I get squeezed to the Earth's surface and exert a pushing force on the Earth's surface that cancels out the pulling gravitational force that I exert on the Earth. If I somehow manage to levitate then the velocity will take a really really really long time to build up for us to notice. | |
| Jan 15, 2019 at 9:25 | history | edited | Steeven | CC BY-SA 4.0 |
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| Jan 15, 2019 at 9:14 | history | answered | Steeven | CC BY-SA 4.0 |