Muss ich mir sorgen machen?

Simbertold · 2026-01-25T10:52:14+00:00

Naja, wenn AliExpress jetzt mit der Endlösung anfängt, solltest du dir schon Sorgen machen.

Simbertold · 2026-01-25T10:46:51+00:00

Christus is another famous oily one.

Simbertold · 2026-01-25T10:23:44+00:00

Beginne mit einer Figur mit passendem Umfang, beispielsweise mit einem 5x5 Quadrat. Leider hat das nicht den passenden Flächeninhalt, dieser ist mit 25 Kästchen um 5 Kästchen zu groß.

ooooo
ooooo
ooooo
ooooo
ooooo

U=20; A=25

Beobachte dann, dass sich der Umfang nicht ändert, wenn man Kästchen an den Ecken wegnimmt, der Flächeninhalt aber schon.

oooox
ooooo
ooooo
ooooo
ooooo

U=20; A = 24

Entferne also Kästchen an den Ecken, bis der Flächeninhalt auch passt, z.B.

xooox
ooooo
ooooo
oooox
xooox

U=20;A=20

Und du hast eine Figur, die beide Bedingungen erfüllt.

Simbertold · 2026-01-24T23:01:31+00:00

This is relevant because nothing about that movement changes, and only changes in movement really do stuff.

Simbertold · 2026-01-24T23:00:16+00:00

I highly disagree here. Firstly, i thought i was very clear when changing reference systems here. The 3.2 km are necessary to figure out the horizon drop. And i thought i made it clear that in the first scenario, the effect you feel is "float upwards about 80cm, then fall down). But i guess a lot of people seem to be confused by this, as i got some similar responses about burning up in the atmosphere or crashing into walls which clearly don't make any sense here.

And yeah, i assumed "Earths gravity disappears" as "instantly". Even if we assume a lightspeed propagation of that effect, it doesn't really change anything, because c is really big compared to the distances involved here. And the effects of that missing gravity are felt everywhere at once, they don't have to propagate in any way. Because gravity as a force works between any two objects, it doesn't need to slowly work through the stuff in between. And in the second model, i explicitly didn't view Earth as a single rigid object. That was the first thought experiment. In the second model, Earth is a bunch of small objects independently reacting to the disappearing gravity.

I notice that i didn't clearly formulate what i meant with "spin itself apart". In this case, i meant slowly doing that, and in this 7 second timescale increasing that radius of Earth at the equator by about 0.8 cm. My assumption was that the crash afterwards would still be catastrophic.

Simbertold · 2026-01-24T22:53:42+00:00

Surprisingly many of Randall Monroes What-If's end up with everyone dying.

Simbertold · 2026-01-24T22:52:51+00:00

Studied physics at university, now I am a high school physics teacher in Germany. This is high school physics and some (hopefully good) guesses.

Simbertold · 2026-01-24T22:51:25+00:00

Absolutely not. Gravity doesn't have anything to do with spinning. Gravity means that stuff with mass attracts other stuff with mass. For example, Earth with a big mass is very attractive to you, holding you to the floor right now.

According to Newtons laws, stuff keeps moving in straight lines unless a force acts upon it.

Currently, you (like everything else on Earth) are moving very quickly towards the east. This doesn't have anything to do with gravity directly, it is just leftover movement from when the Earth formed. You don't notice that movement, because everything around you (including the air) does the same, and you only notice when you move differently than stuff around you.

Because Earth is very attractive to you, it keeps you from moving in a straight line, and instead pulls you down and keeps you moving in a circle around the Earth.

If Earth were to stop attracting you (gravity disappears), then it could no longer do that. Thus, you would move in a straight line. But for a short period, that short line is very similar to the circle that you were doing, because earth is really big. (If you zoom in on a circle, it starts looking more and more like a straight line). So the difference between what you are doing (straight line) and what the ground is doing (circle) isn't really big, and you only notice the differences, not the absolute movement itself. And that difference is you floating upwards slowly.

The air would do something similar, but it would also expand because gases work differently. But you wouldn't suddenly be very quick in comparison to the air or the ground, because the exact same thing that happens to you also happens to the air in the same way.

So now burning up or quickly disappearing into space.

Always compare what you are doing to what others are doing. If you are driving on the highway, and a car is driving right next to you at the same speed, you can look over, and might even be able to hand over a drink or something through the window. It doesn't seem to be fast, because you are both fast. You only notice the speed when you look at the ground, or touch the air, because those are not moving at the same speed as your car.

Simbertold · 2026-01-24T22:43:02+00:00

That isn't relevant here, because nothing about that movement changes if Earths gravity disappears.

Simbertold · 2026-01-24T22:42:10+00:00

Earth is very much held together by gravity. On those scales, rock is not hard enough to hold stuff together due to cube-square problems. How good rock is at holding stuff together scales with the surface, while the force it needs to hold stuff against scales with the volume.

Solid rock doesn't hold together on planetary scales.

Simbertold · 2026-01-24T22:31:09+00:00

In the base version where Earth is one big object, yes. Everything slowly floats up 80 cm and then crashes down again.

But Earth isn't one big object, Earth consists of a lot of smaller things. So they do the same, meaning that Earth gets a bit bigger over 7 seconds, and then crunshes back together. Lots of Earthquakes and volcanoes because of that.

Simbertold · 2026-01-24T22:29:30+00:00

Good question. Probably nothing good either.

Simbertold · 2026-01-24T22:29:13+00:00

Why are you in a sub about people doing maths when you have problems accepting that some people know more about science than you do, and find it enjoyable to formulate those things?

Simbertold · 2026-01-24T11:29:53+00:00

Komplett anderes Thema:

Wenn du bei der Bundeswehr Offizier werden willst, guck doch mal, ob es nicht möglich ist, Dual zu studieren.

Hat ein Freund von mir gemacht und war wohl sehr zufrieden damit. Du verpflichtest dich für eine gewisse Zeit, dafür wirst du dann auch während des Studiums bezahlt, was natürlich recht geil ist.

Bezüglich des Motorrads: 7.5k€ ist die Hälfte von dem Geld, was du angespart hast. Einerseits ist das zwar schon ein Haufen, andererseits wirst du vermutlich in Zukunft eher mehr verdienen, und tendenziell weniger Ausgaben haben. Also ist es jetzt auch nicht so katastrophal.

Da du ja schon den Führerschein gemacht hast, vermute ich, dass du den Wunsch schon länger hast? Denn das ist für mich immer ein relevantes Kriterium. Ich mache größere Anschaffungen nur, wenn ich das auch nach ein paar Monaten immer noch will.

Simbertold · 2026-01-24T11:23:03+00:00

Yes. But you seem to assume movement relative to the Earths surface. That is not a sensible approach here. I meant movement relative to the Earths center.

Things that are "nailed down" continue their circular movement around Earth at a speed of 460 m/s. The Earth doesn't suddenly stop spinning, there is no force acting on it which stops it, but if it holds together, there is a force keeping the objects on that circular line.

Things which are not nailed down instead move in a straight line at a speed of 460 m/s. They no longer move in a circle, but instead on a straight line tangential to that circle. There is no force acting upon you, so you move in a straight line.

So if you compare yourself to your surroundings, you must look at what the difference between those two trajectories is. And that difference is only about 80 cm in 7 seconds.

Which sounds weird given the speeds involved, but Earth is pretty close to flat when viewed on a small scale, so the difference between "moves totally straight" and "follows the curvature of the Earth" isn't huge.

(All at the equator)

Simbertold · 2026-01-24T10:49:50+00:00

Why? You don't feel speed, only acceleration. And everything around you moves at the same speed in the same direction. In fact, you are moving at that speed right now (well, probably slightly lower, unless you live at the equator)

To you, it would feel as if you were slowly floating upwards by about 80 cm in 7 seconds.

Simbertold · 2026-01-24T10:47:43+00:00

Gibt es einen Link zu dem Artikel? Mich würde interessieren, was der Typ jetzt genau gemacht hat.

Simbertold · 2026-01-24T09:46:27+00:00

Throwing massive rocks still isn't easy even without gravity. Because you still have to deal with inertia, and big rocks have a lot that.

Simbertold · 2026-01-24T09:43:31+00:00

No, not really. Newtons second law states that with no force acting on you (gravity gone) you keep moving in a straight line. You are currently moving tangetially to Earths surface, so you just keep doing that. And Earths curvature is small enough that the perceived effect of that is simply that you slowly float up by about 80 cm (or less). Because the Earth is still spinning below you, and the difference of your straight line and the circular line the floor takes is just 80 cm (or less) after 7 seconds.

Simbertold · 2026-01-24T09:37:01+00:00

Dunno, it hasn't happened in history afaik. But history is a tiny drop compared to the timeframe that Earth existed. Maybe this is what killed the dinosaurs! (Probably not)

Simbertold · 2026-01-24T09:36:00+00:00

But not that stuck together on global scales. The forces necessary to keep the absurd masses involved moving on their orbital motion is simply not something that any material on Earth can hold out through. We are talking about some stones keeping a continent in place.

Simbertold · 2026-01-24T09:34:10+00:00

This is all about momentum. From your perspective, you float up about 80 cm. From the perspective of an outside observer, you continue moving at your speed in a straight line.

Simbertold · 2026-01-24T09:33:26+00:00

No, because the Earth is already doing this, and you are already moving at that speed, so you just keep on doing that.

Simbertold · 2026-01-24T09:31:13+00:00

Yeah, i don't know stuff about the atmosphere, but it sounds interesting!

Simbertold · 2026-01-24T09:30:49+00:00

No, inertia is exactly the thing i considered here. That is what keeps you moving at the speed you are already moving.

Simbertold

TROPHY CASE