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Wouldn't it be cool if giant monsters were on giant planets? Of course it would be, but unfortunately physics doesn't really like that idea. Big planets make things on them need more support, so being big sucks on big planets. It's alright on teeny ones, but bad on big ones. You'd also probably want high pressure on the planet, and low temperatures, but let's forget about that.

So how could one make it not suck to be big on such a planet.

Well....we could make the planet spin faster. Now, these big monsters, effectively, weigh a bit less. They would have to be slow, because the energy to move them (due to inertia) would be the same, so you'd probably looking at creatures with big support structures and less muscle adjacent structures?

Problem, of course, people have asked about how fast the earth would need to spin to make things weightless, of course that would destroy a planet...but what if the question was, instead,

Edit: To keep it simple, I'd like to know if a planet could (effectively) offset 10% of its gravity through rotating fast, without flinging itself into a cloud of space dust.

Cyn
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Ravitheravian
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    "cool if giant monsters were on giant planets", why not? Buoyancy solves a multitude of issues with size and mass - it depends what they're floating in. How do you mean "chthonian planet", do you mean that all the life is underground - or are you talking spirit beings of the underworld here? – Escaped dental patient. May 23 '19 at 17:54
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    Welcome to WorldBuilding.SE! There's a lot of different questions you're throwing at us here, it might be better to try and narrow this down to one specific thing that you want us to answer. – F1Krazy May 23 '19 at 17:56
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    Hey, Ravitheravian welcome indeed, when you have a few minutes, please take the [tour] and read up in our [help] about how we work: [ask]. At the moment it's not clear what you're asking, could you [edit] the question to clarify? – Escaped dental patient. May 23 '19 at 18:00
  • Hi, welcome to Worldbuilding. Stack Exchange’s model is “one specific question, one specific answer” so this may be closed for being too broad. Can you [edit] your question to only have one question to make it clear what you’re asking? You can always ask more. Visit the [help] if you’re unsure. There is a Sandbox on [meta] where users can develop their questions to make sure they are suitable for the main site. Also, we have a list of resources which may answer any broader questions about worldbuilding: https://worldbuilding.stackexchange.com/questions/143606/a-list-of-worldbuilding-resources? – Liam Morris May 23 '19 at 18:03
  • hmm, yeah, I think I can give it a quick, if drastic, edit. – Ravitheravian May 23 '19 at 18:11
  • @Ravitheravian : Works for me. Those who vote to close - please comment to make your point clear to the OP so the issue can be addressed. – Escaped dental patient. May 23 '19 at 18:25
  • I completely revamped your tags to match the question in your post (not the backstory...you may want lower gravity so you can have bigger monsters, but they're irrelevant to the question). If you or any one else disagrees with my changes, have a go! (P.S. don't do a rollback cause I also fixed some typos, unless you don't want the corrections.) – Cyn May 23 '19 at 19:13
  • A big problem is going to be lack of atmosphere, as reduced gravity means reduced atmospheric hold. – kleer001 May 23 '19 at 18:23
  • If you're open to solutions that don't involve silly rotational speeds, I have one... – Starfish Prime May 23 '19 at 19:56

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Run to your local used SF book store and find "Mission of Gravity" by Hal Clement.

Meskin is somewhat over Jovian mass, with most of the mass in a relatively small core. The planet spins once every 10 minutes giving it the shape of a poached egg and an equatorial diameter several times its polar diameter. The net result is 3g's acceleration at the equator and 700 at the poles.

Brythan
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Sherwood Botsford
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Yes

Here's the non-mathy version: A planet can spin as fast as gravity will allow. That is, the "speed limit" on angular velocity is the speed at which the outward centrifugal force (rotational inertia for the nitpickers) balances the inward gravitational force. So by definition your condition that 10% of the gravity be offset is achievable and probably doesn't come close to even meeting the caveat below.

Notes and Caveats

As a planet spins it will begin to bulge at the equator and squash at the poles (Earth's radius is roughly 20km larger at the equator). This is a consequence of the aforementioned centrifugal force and the fact that planets exist in hydrostatic equilibrium (act as a fluid at rest) over long time spans. The bulging of the equator as angular velocity increases may change the point at which the planet ceases to be a planet, but this will be a secondary effect.

The centrifugal force will be at maximum at the equator and decrease with the cosine of latitude to zero at the poles. This means the apparent gravity will be lower at the equator but this effect will diminish further away. So your creatures may survive in a certain latitude band.

The direction of the centrifugal force will be directly outward at the equator and vary to being perpendicular to gravity at the poles (of course the magnitude of the force will be zero at the poles too - see above note). The most apparent effect of this is that in the mid-latitudes the ground will feel tilted because gravity will be acting downward and the centrifugal force will be acting outward at an acute angle to gravity.

ben
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A thick, heavy atmosphere would do the trick

You don't need to resort to a spinning planet. If your giants are made of material only marginally heavier than the atmosphere, the atmosphere would support most of their weight, and very large sizes would be possibles. Think of blue whales in the ocean, the largest animal ever in existance, with a mass of up to metric 173 tons (the heaviest reported) or possibly even more.

Klaus Æ. Mogensen
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