1. PenTrotter
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    PenTrotter Member

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    Resources for physics

    Discussion in 'Setting Development' started by PenTrotter, Feb 4, 2013.

    I'm starting a peice up in my head, but I have a question. It is in an alternate universe with an alternate world, landforms, etc. But it has physics similar to Earth's, as I am not a celestial being capable of altering perception in itself, so that would just be a better thing to do. That being said, would there be any restrictions as to how things can form, the height of things, density, gravitational pull on landmass, etc., is there any resources I can find that would guide me with these guidelines of earths universe? Laws of physics almost.
     
  2. Cogito
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    Cogito Former Mod, Retired Supporter Contributor

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    There are, but only if you know what to look for. Google will help guide you to answer specific questions, but it's up to you to ask the right "what if"s.
     
  3. minstrel
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    minstrel Leader of the Insquirrelgency Staff Supporter Contributor

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    Any high school science or physics textbook should have the information you need explained simply.

    Here's stuff to get you started: Yes, assuming things on your planet are made of Earth-type materials, gravity will definitely affect how high things can be. But the force of gravity depends not just on the mass of the planet and the object in its field, but on how far from the center of the planet the object is. So you can imagine planets that are huge, much bigger than Earth and more massive, but if they're less dense, it's possible for them to have less gravity. On the other hand, you can have smaller planets than Earth that are EXTREMELY dense, but with less mass than Earth, that have more gravity than Earth.

    Be aware, also, that objects in a stronger gravitational field will fall faster - that is, the acceleration due to gravity will be higher. If you have people from Earth going to a planet like that, they might find that fact harder to deal with than simply their increased weight.
     
  4. Xatron
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    Xatron Contributing Member

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    Yes, for example you can't have a bird with 25m wing spread because it's bones would have to be made of silk or something. Equally you can't have people 4m tall because their cardiovascular system would fail after a few short years.
    That is if you want to make it faithful to Earth's physics to the letter. If your world has the element of magic or something of the sort you can improvise much and it won't need to adhere to so many rules. Or you can make the species you want (i assume they won't all be human since it is a different world) made with superior genetic material so they can defy a few rules of nature.
     
  5. Cogito
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    Cogito Former Mod, Retired Supporter Contributor

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    I wouldn't say it's all high school physics. How steep a mountain slope can be sustained is beyond high school physics. It's advanced material science along with an understanding of the gravitational and tectonic forces present, and the fluidity of the landscape material under those conditions. Not trivial.

    Planetary climate is nontrivial as well. Ocean to land ratio, axial tilt, orbital eccentricity, the presence of natural satellites, and atmospheric composition all contribute.

    Some details aren't important to nail precisely. Still it does help to understand the influence and at least be able to make a first-order estimate of plausibility. No weird planetary orbits that turn a lava-covered furnace of a planet into an ice field for one month every thousand years.
     
  6. Xatron
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    Xatron Contributing Member

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    If the environment and rules of nature play a big role in your story you should research it further. If though it is just the background setting and is not actively involved in your story then i believe almost no reader will nitpick at one or two wrongly adapted characteristics of your planet.
     
  7. henmatth
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    henmatth Member

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    Another thing to remember is that our gravitational pull has a lot to do with our distance from the sun and our rotations around it. So if you are building an alternative universe, with an alternate planet- you may also want to have an alternate star (or 'sun') for that planet to be aligned with. We as humans are quite blessed in the fact we live on a planet that is at just the precise area for our existance. Scientists typically look for 'earth like planets' that are rotating at a similar speed and distance from another star. Just a thought ;)
     
  8. tionA
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    tionA Active Member

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    What rubbish!

    This is not true. See minstrel's answer:

    ''assuming things on your planet are made of Earth-type materials, gravity will definitely affect how high things can be. But the force of gravity depends not just on the mass of the planet and the object in its field, but on how far from the center of the planet the object is.''


     
  9. henmatth
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    henmatth Member

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    Okay, perhaps I worded that wrong. I suppose our gravitational pull is not so much defined by the distance from the sun, but in order for things to form in the same general way- we would need to be approximately the same distance. Our temperature, atmosphere, and sun location has a lot to do with our landforms and how they have come to exist. I'm by no means a science major, so I suppose my reply on the gravitational pull was misinformed- but I thought I had recalled a similar theory mentioned in a physics class. Sorry, I stand corrected.
     
  10. minstrel
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    minstrel Leader of the Insquirrelgency Staff Supporter Contributor

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    The distance our planet is from the sun is very important, because it puts us in a narrow band where the temperature allows for liquid water. If we were too close to the sun, the temperature would be so high that all the water would be vapor. If we were too far from the sun, it would be so cold that all the water would be ice.

    Liquid water is very important in the formation of features of the landscape because oceans, rivers, and rain erode the land. It's also important in that it allows plant roots to absorb nutrients from the soil - we would have very different flora here on Earth, if we had any life at all, without liquid water.
     
  11. Cogito
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    Cogito Former Mod, Retired Supporter Contributor

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    Yes. It's called the Goldilocks Zone. and depends on the spectral type and luminosity of the star. Of course, it applies to life based on the kinds of chemistry we are familiar with. As for geographic features, similar shapes could be carved from the landscape of any planet with a lithosphere (a rocky surface) by liquids other than water, ranging from liquid nitrogen carving channels through a lansdscape of frozen ammonia and water ice, to rivers of molten metal on a very hot planet orbiting close to a star.

    In the Solar system, Venus lies in the Goldilocks zone, but it lacks a natural satellite like our moon, and so has a denser atmosphere rich in greenhouse gases, making it a furnace=like environment too hot and corrosive to support terrestrial life. Our moon's tidal forces have stripped away excess atmosphere that would have made Earth hostile to life as well, although probably not as hot as Venus.
     
  12. tionA
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    tionA Active Member

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    What rubbish!

    A planet does not need to be close to its star to have liquid water!

    Internal heat as a result of tidal forces from other planets or internal radioactivity and volcanism can also contribute to a planet's liquid water.

    Just look at Jupiter's moon Enceladus.
     
  13. tionA
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    tionA Active Member

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    This is by far the worst rubbish I've read today!
     
  14. minstrel
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    minstrel Leader of the Insquirrelgency Staff Supporter Contributor

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    Enceladus is a moon of Saturn, not Jupiter.

    Because Enceladus is an inner moon of a large planet, it orbits very quickly - it only takes 1.37 days to complete an orbit. This means it is subject to very large tidal forces, and those could be enough to melt water, even though the surface temperature of Enceladus is about -200 degrees Celsius. That's way below freezing, BTW.

    But we're not talking about moons of large planets. We're talking about planets themselves. Earth isn't subject to large tidal forces from the sun. Our tides are caused because we have a moon that's very large compared to the size of our planet, as these things go. If the moon was a lot smaller, or if we had no moon at all, we'd have insignificant tides - the sun isn't enough.

    If you broke Enceladus away from Saturn and set it in orbit around the sun, the same distance from the sun as Saturn, but far away from Saturn (on the other side of the sun from it, for example), it would not have the tidal forces that keep it warm enough to have liquid water.

    So, yeah, for a planet that isn't hugely radioactive to have liquid water, it has to be in the Goldilocks zone.

    Do some research, and some decent thinking, before you call someone else's post "rubbish."
     
  15. tionA
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    tionA Active Member

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    lol I bet in your desperate need to reply you learned a whole lot of interesting stuff, didn't ya?

    You're welcome!
     
  16. minstrel
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    minstrel Leader of the Insquirrelgency Staff Supporter Contributor

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    Actually, all I looked up was the temperature and orbital period, because I wanted reasonably accurate data. I already knew about Enceladus - I subscribe to Scientific American and visit some pretty cool websites. ;)
     
  17. Cogito
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    Cogito Former Mod, Retired Supporter Contributor

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    [​IMG]
     
  18. Pale Writer
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    I have recently watched a documentary called 'Alien Planet' which might give you an example of what you can look into trying. They deal with gravity/air density/plant life/animal adaptations on worlds that live in the 'Goldilocks Zone'. Like any world building, even alien nature has rules or co-exists/evolves so you can't simply place something for no reason. For examples if it rains aluminum it has to come from somewhere, and then what nutrients do the lifeforms take from this offering.

    For example in the docu/movie there was only one large sea but it developed a 'skin' of sorts to protect from losing its remaining moisture. It isn't quite water but rather a living organism which can feed. Your imagination can expand, but life/nature/etc should have purpose.

    Best luck

    Pale
     
  19. PenTrotter
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    PenTrotter Member

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    Thank you for all the great replies (wow this forum is far better than I thought it would be) I'll be looking into gravitational physics and that whole water argument, also trying to expand my planet as mich as I can in the reaches of physics,and I'll be looking into that movie, 'Alien Planet', And tionA, chillax a bit.
     
  20. PenTrotter
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    PenTrotter Member

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    and this is telling me?
     
  21. minstrel
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    minstrel Leader of the Insquirrelgency Staff Supporter Contributor

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    It means "Don't feed the trolls."

    The comment was meant for me.
     
  22. tionA
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    tionA Active Member

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    What rubbish!

    The comment was meant for me!
     
  23. niallohagan
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    niallohagan Member

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    Gravity depends on mass. More massive objects have a stronger gravitational field. Jupite is more massive than Earth but is only 1/4 as dense yet its grav field is much bigger than Earth's.
     
  24. minstrel
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    minstrel Leader of the Insquirrelgency Staff Supporter Contributor

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    Apologies for nerdiness:

    Of course gravity depends on mass. But it's also inversely proportional to the square of the planet's radius. I just did the calculation, and if Jupiter had a mean radius of about 114,000 kilometers, it would have about the same surface gravity as Earth. Jupiter's mean radius is about 70,000 km, so that means if Jupiter had a radius only 1.62 times what it now is, it's gravity would be about the same as ours.

    For comparison, look at Saturn. It has 95 times the mass of Earth, but just about the same surface gravity. That's because it's so huge that it has a very low density - less than water.

    /nerdiness
     
  25. tionA
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    tionA Active Member

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    Ouch!

    Minstrel just took you to school!
     

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