Gravity

Started by Taronyu, December 28, 2009, 10:09:11 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Taronyu

So, we've seen that the megaflora and the fauna of Pandora are just plain massive, and taller. This is claimed to be due to a lower gravitational force - we can assume, then, that Pandora is smaller than Earth. I calculate that Pandora is just over half the size of earth, as that would give 40% of the gravity. Of course, 60-80% would probably make more sense, making Pandora around 3/4 fifths of Earth's size.

What i want to know is how the neighboring planet would have affected Pandora, for one. The tides on the ocean, and in a particular the waves, would be massive. Truly, truly massive. I don't think the shot we're shown accurately represents this, unless those cliffs mark a coastal shelf that is immediate.

Another issue: Why can human's walk the same way? Surely they ought to be bouncing in their steps. This annoys me, but I understand due to monetary constrictions. What I do like, very much, is that Jake Sully atrophied at an alarming rate - much less than one would expect, in three months of inactivity. This was to the good.

Ikran

You'll find the answers to these questions in An Activist Survival Guide. You can browse the book here:

http://browseinside.harpercollins.com/index.aspx?isbn13=9780061896750

Taronyu

Quote from: Ikran on December 28, 2009, 10:17:52 AM
You'll find the answers to these questions in An Activist Survival Guide. You can browse the book here:

http://browseinside.harpercollins.com/index.aspx?isbn13=9780061896750


Cheers. Didn't realise this was online yet. :)

Toruk Makto

Well, the online version is very abridged. The actual book is much much larger.  I read it into the wee hours of the morning last week. I am wickedly indulging my Avatar addiction at work right now and the book is at home. I will look through it again this evening to see if any of your questions are covered there.

Lì'fyari leNa'vi 'Rrtamì, vay set 'almong a fra'u zera'u ta ngrrpongu
Na'vi Dictionary: http://files.learnnavi.org/dicts/NaviDictionary.pdf

Unil täftxuyu

by the looks of that, Pandora isn't that much smaller than earth at all and probably only has a gravitational difference of 5-10% rather than 20%, it would be mostly unnoticable. (I'm not going to get in to it, but no one really knows how gravity works, so size may not matter)

Taronyu

Yeah, the online version wasn't entirely helpful.

It has to do with mass. They say that Pandora is smaller, but with higher gravity due to a heavier core. It's interesting.

I still think tides would massively fail. I've spent hours and hours looking at geology books for my own terraforming, and those things are impossible to successfully calibrate without terrestrial gravity.

Unil täftxuyu

i'm too tired to make any sense of anything right now, haven't slept yet, but i'm going to go out on a limb here and say that perhaps the planet that pandora orbits would affect the tide rather than having a satellite of its own.

Toruk Makto

#7
Usually, large tidal changes also require large bodies of water. Due to Pandora's proximity to the gas giant exoplanet Polyphemus and the resulting gravitational stresses, the tectonic plates of Pandora are very fractured, creating a complex mosaic of land and water. Besides creating moderate weather, it probably also creates minimal tidal effects in the seas.

Lì'fyari leNa'vi 'Rrtamì, vay set 'almong a fra'u zera'u ta ngrrpongu
Na'vi Dictionary: http://files.learnnavi.org/dicts/NaviDictionary.pdf

Doolio

if the gravity was only 5-10% weaker, i doubt that the na'vi could be so nimble given the fact that they are about four meters high.

just my 2c
...taj rad...

Unil täftxuyu

the gravity would only be 5-10% because humans move so earth-like on pandora, but the Na'vi are subject to the planets different atmosphere, their own different physiology and many different factors. they have carbon fiber reinforced bones for one  8)

Ikran

According to the Survival Guide, gravity is only 20% weaker. I find 0.8 g to be a large number for a moon with those huge animals and plants! After watching the movie, I was guessing 0.5-0.6 g... ???

Doolio

#11
yes, that has crossed my mind, maybe they are less massive than the similar sized earth creatures.

but i've just checked the online version of 'confidential report' (thanks ikran:) ) and it says this:

-diameter (km):
earth: 1275.27 (clearly an error, so 12 752.7)
pandora: 11 447

-mass:
earth: 1
pandora: 0.72

-surface gravity:
earth: 1
pandora: 0.8

-atmospheric density:
earth: 1
pandora: 1.2

-surface pressure:
earth: 1
pandora: 1.1

so it seems that is 20% weaker after all, but you are right in one thing, there are many other factors...but i still don't know how these factors corelate and influence each other and the planet biosphere...any biologists? geologists? :)


@ikran:
yes, but maybe gravity influence is changed exponentially? or these other factors (pressure, density...) play significant roles, so, i call on science buffs to elaborate:)
...taj rad...

shiaru

#12
Science buff over here! Ok why are the animals so big???

Well that is a simple one, even though the gravity is an important factor determining the size of an indigenous species it is not the only one. Now to demonstrate my point think of these not so well known animals called Dinosaurs... you know the little guys who were kinda big as a three to four story building.

here is a pic to scale:


Ok now If on earth we could have those guys on a moon where gravity is less and we got a diet of god knows what kind of proteins, well their size could very well be gigantic by human standards.  That guy in the pic was 7 to 8 meters tall from the leg to where neck started.

now my good buddy here the Hammerhead Titanothere was only six meters in height, and eleven meters long.
Here is a picture of him:



Now that we do a comparison it does not seem that far fetched does it ?
~Oe lu tanhì taronyu.~

Ikran

You're right about the size of animals, Shiaru, but I keep wondering about the huge trees. With only 0.8 g, it seems to me that the weight of Kelutrel should be enormous, despite the hollow structure. Anyway, I understand that a world with 0.5 g would be much more difficult to portray in a film.

Doolio

yes, the animals are not the problem, i myself thought of the dinosaurs instantly:) also in the time of dinosaurs, vegetation was thriving and the trees were quite large given the somewhat different atmosphere.

what catches my eye is that na'vi are much more agile than any human, maybe like a human-sized ape. also, the titanothere seemed pretty quick to me. i understand that is because of their different physiology and biological and atmospoheric factors, but what interests me is it possible to explain relying on the info in that table that i typed from the book.
i mean something in the lines of 'blablah higher atmospheric density blahblah yields less/more massive organisms blabla':)
...taj rad...

shiaru

I've been wondering about the trees as well so far the only conclusion i can come up with it that they are not made of wood. And by wood I mean cellulose fibers and lignin. I think they are rather derivative of nanofibers perhaps similar but not equal to the bone structure of the Na'vi. This would enable it to grow larger than anything on earth and be able to support itself since its total weight is not the same as it would be if it was our kind of wood.

And it is possible to describe Na'vi as more agile than humans because is like comparing a cheetah to a wolf, a wolf is made to run for long periods of time at a constant speed, while a cheetah is made to run faster than any animal for a short period of time. Na'vi evolved in Pandora and thus are better suited to live in there.
~Oe lu tanhì taronyu.~

Toruk Makto

... and they look like they're in pretty good shape.  ;)

Lì'fyari leNa'vi 'Rrtamì, vay set 'almong a fra'u zera'u ta ngrrpongu
Na'vi Dictionary: http://files.learnnavi.org/dicts/NaviDictionary.pdf

MOUNTAINBANSHEE

didn't you guys know that the na'vi have 4 times the strength per cell !!!
join our real life tribe! here(And yes, it will be a real tribe in the real world, not a role play tribe)

Reronsem Si

Quote from: shiaru on December 28, 2009, 04:31:19 PM
And it is possible to describe Na'vi as more agile than humans because is like comparing a cheetah to a wolf, a wolf is made to run for long periods of time at a constant speed, while a cheetah is made to run faster than any animal for a short period of time. Na'vi evolved in Pandora and thus are better suited to live in there.

I think a lot of people are also confusing size with lack of coordination. One thing I pondered was that if the environment on Pandora is made much like a brain with vastly more neurons, then perhaps the biological make up of the Na'vi brain and body also has more neurons than humans. Allowing for more independent reflexes, much like you twitch your eyes or body automatically when something comes at you, it's very possible that there are independent nerve centers to piggy back motor control. Much like very very large dinosaurs equipped with nerve clusters in the lower spine to assist in walking.

Motxokxen

you know it's really hard to tell how gravity influences evolution, considering the only evolution was have to reference is our own and we've had the same gravitational force since the earliest life forms.

As for people walking. .8 gravity is not a huge difference, is you take my approx weight ( 140 and multiply my .8 then i'd weigh 112 pounds) but I'm skinny, so the average  of 160 times .8 would be 144. yes you would feel lighter, but you would not bounce.

compare that to the moon, with has .167g, even mars only has .38g