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A while ago I asked this question about if a planet 1/5th larger than earth could remain earth like. The top answers all seemed to agree that while the planet could be that much larger and still only have 1g gravity, it would be so poor in heavier elements as to be nothing like earth.

By increasing the density to be on par with earth, this planet's surface gravity would be 1.249g.

The main issue i have is that I want to be able to have things built on earth in real life be able to still work on this planet without issue. As the setting isn't supposed to have it as being colonized from elsewhere but as more of an alternate earth type thing. I don't know if that level of gravity increase would make things operate with significantly different characteristics

So, would 1.249 times earth gravity prevent things from working as they do on earth or not?

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    $\begingroup$ I'm sorry, but I tried to comment, then answer, then I realized there's simply too much that falls under the headers of "engineering" or "vehicles and structures." Worse, the word "properly" has so many possible interpretations that everything fell apart. So, VTC:Needs More Focus. Here's your problem: if you want an Earth-like planet you need to basically duplicate Earth. Anything you change from that baseline has consequences for everything. It's impossible to give you a single number that deals with everything other than 1G +/- 1%. You want a simple answer to a very complex question. $\endgroup$
    – JBH
    Commented Mar 22 at 16:53
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    $\begingroup$ An example: here on Earth we design a bungee cord with safety wire and a braking system to allow (*ahem*) people of questionable judgement 😎 to jump off bridges. That's 1G. Let's use 10G for easy math. 10X the weight of the body. 10X the weight of the bungee and safety wire. 10X the stress on the braking system. That means seriously redesigning the whole experience just to keep the jumper from dying on a 10G world (ignoring what it would do to their internal organs). Grab today's equipment and move it to another planet... 1G +/- 1% so you can use the same liability forms. $\endgroup$
    – JBH
    Commented Mar 22 at 17:05
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    $\begingroup$ Better, but still too broad. Short buildings might not have problems. Tall buildings in earthquake zones might. Incandescent light filaments might not work. LEDs wouldn't have a problem. Car tires will wear faster, the suspension is probably OK, but the seat belts might not be. Every scale's maximum weight is now wrong and they might be completely off since the spring is balanced against 1G. I'm not convinced this is answerable due to the Book Rule. The range of engineering influence is absolutely massive. Is this scoped by colonization? A magical shift in Earth's mass? Why everything? $\endgroup$
    – JBH
    Commented Mar 23 at 17:31
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    $\begingroup$ Sorry, but I'm with @JBH on this one, there are just too many categories of objects, some of which will be fine and some of which will be inadequate or changed in some way, even if atmosphere and everything else is unchanged. Tents, cookers, ranged weapons, mining equipment, climbing gear, medical diagnostics, drugs, SCUBA and other diving gear, refineries, factories, construction plant, plumbing... for some a few paragraphs might answer, other subcategories would require a book each. Need some idea what is being taken on spaceship (or through magitech gate). $\endgroup$ Commented Mar 24 at 3:49
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    $\begingroup$ Considering the staggering breadth of the question, this falls into the infinite list category. See: Catalogue of question types for context of that. $\endgroup$ Commented Mar 24 at 4:08

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If all you're worried about is structural engineering, you can push gravity way up, far beyond what humans can tolerate. Buildings here on Earth aren't built anywhere near the limits of the underlying materials -- instead, engineers try to figure out how little material they can use without having anything break. If you need a car to drive on a 10-g planet, you just beef up the suspension a bit, increase the pressure in the tires, and use thicker pieces of metal for the frame.

If you want to transplant Earth structures unmodified to this world (say, pick up the Brooklyn Bridge, set it down spanning an appropriate-sized river, and start driving Earth-import cars across it), that's a different matter. In general, you can go up to about 150% of Earth's gravity. Large buildings tend to be built with a safety margin of 1.5x-2x, so you'll be using up your margin (and seeing the occasional collapse). Small buildings tend to be stronger in proportion, so a one-story house could probably tolerate a 2-g or even 3-g world, and the typical passenger car can go up to four times Earth's gravity with just a stiffer suspension and better tires.

Humans are actually your limiting factor on a heavy world. A standing human can't handle more than about 1.5g for an extended period; acceleration tolerance when lying down is considerably higher.

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  • $\begingroup$ Would there be any other considerations for aircraft ? $\endgroup$
    – OT-64 SKOT
    Commented Mar 22 at 3:38
  • $\begingroup$ Houses may be built with that kind of support for their own weight, but snow could be a very different matter. There are plenty of houses that you suddenly put under even 50% more snow load and they are going to be in trouble. $\endgroup$ Commented Mar 22 at 15:45
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    $\begingroup$ If you need a car to drive on a 10-g planet, you just beef up the suspension a bit, increase the pressure in the tires, and use thicker pieces of metal for the frame. It's not that simple at all. Just the increased heat created by over pressurizing the tires and moving the car at speed at 10G would reduce the lifespan of today's tires to next to nothing (or it would reduce the max speed to next to nothing) and that's just one variable. Most of the electrical infrastructure can't operate under 10G without massive redesigns. -1 for not having nearly enough insight into engineering. $\endgroup$
    – JBH
    Commented Mar 22 at 16:56
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    $\begingroup$ @OT-64SKOT, changes to aircraft depend not just on gravity, but also air density and composition, and the availability of fuels. It's not possible to make a blanket statement (flying on Earth is very different from flying on Venus, despite the surface gravity being similar). $\endgroup$
    – Mark
    Commented Mar 22 at 21:24
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With current technology, it is possible to make things that work with 1.25 times more gravity. For example, you can build a bridge or a house for your planet just by using the right dimensions for structural or mechanical elements. This way building a 3 story building in your planet won't be harder than building a 4 story building on Earth.

If you want to move Earth devices to your planet, then you may find some problems.

For example, let's suppose you move an small van to your planet and that on Earth that van weights 2 ton when empty and it can carry a 1.5 ton load. Therefore, the van is fine while the total weight on the wheels is 3.5 ton or less. In your planet the empty van weights 2.5 ton, so it can carry just 1 ton load instead of 1.5 ton.

For different vehicles (or other devices) the numbers might be different, and you may find that after adjusting for the increased own weight there isn't any remaining capacity for payload.

Of course, we can't always trade payload for the increased own weight. In the example of the van, brakes are likely to work better in your planet while engine supports may fare worse.

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There is one important device which may work on another planet, yet must be adjusted to do so: GPS satellites. First, if you take the GPS satellites and just launch them into orbit, the satellites will not work accurately and will lead drivers and pilots off their intended track.

Global positioning systems need such a level of precision, that even the insignificant (in our daily lives) relativistic effects of time dilation due gravity and satellites velocity are accounted for. Failure to do so may result in accumulating measurement errors in the range of a few miles. At any other gravity, and axial rotation, geosynchronous satellites must be set at a different altitude, affecting time dilation due to velocity. Time dilation at the surface of the planet is higher, due to a higher gravity. So, feeding the rotation period into the parameters would not be enough for accurate GPS results.

Another aspect which must be accounted for is heat convection. Did you see what a candle flame looks like on the ISS? It looks like a glowing ball, because combustion is very slow. The hot air does not rise as quickly in the presence of a weak gravity, so fresh air does not replace it quickly as well. Combustion is therefore slower. However, at a higher gravity convection currents are faster. Imagine there is a fire in a warehouse. Hot air rises quickly and fresh air descends towards the fire and feeds it. Firefighters will have to work much harder to put out the fire. However, many devices which work using convection would work even better at a higher gravity. For instance, separation of different solids/liquids of different densities would work faster under a higher gravity. Sewage water treatment facilities, hydroponic systems, drainage canals and the likes will work better as well. Agricultural fields would drain more quickly after heavy rains.

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There’s a whole list of devices that would fail functionally rather than structurally under higher gravity. Pendulum clocks, water clocks, hourglasses, most scales (those which are calibrated in grammes rather than newtons, and aren’t balance scales), and so on. Basically, measuring devices made assuming that gravity is 9.8m/s².

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Some machines would be no problem. Like, I don't see any reason why a can opener built in 1G would not work fine in 1.25G.

Anything that relies on gravity being at a specific level would presumably not work. Like, a clock that uses a pendulum to regulate its speed would not work properly. But I think the number of such devices is pretty small. Perhaps the biggest issue would be aircraft. They're designed for Earth gravity, where the air passing over the wings produces enough lift to offset gravity. With higher gravity it would be questionable if they'd generate enough lift.

I'm trying to think of an example where a machine depends on gravity having a specific strength in more subtle ways. I can't think of any, but that's not to say there are none.

A different issue would be the stress put on mechanical parts. Higher gravity would create more stress. At extremes -- I think way beyond 1.25 G, any machine would be flattened into a pancake. So I presume at 1.25 G some more delicate parts would be deformed by their own weight. This would likely most affect small mechanical objects. I'm not sure what examples of this would be.

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