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Giant/Giantess Fantasy Physics, Questions

  1. Sep 21, 2013 #1
    Giant fans!

    I have some ideas and questions about the physics surrounding mega-giant/giantess fantasy stories, comics, etc., and would like to share some ideas and ask some questions.

    The main question is this: What would it feel like to be 3,000 feet tall on Earth -- with the same proportions and density as humans, but 500 times taller?

    Fun question, huh?

    Well, I'm totally convinced of two things:

    1. You'd feel 1/500th the gravity that humans feel.

    2. The speed of any moving object would seem like 1/500th the speed to you, compared to a human experience.

    What do I base these two premises on? Simple: if an object accelerates from 0 to 1000 MPH in 10 seconds, then it accelerates at 100 MPH/sec, or a little less than 5 G's. But from the perspective of you, the mega-giant, it would seem to go from 0 to 2 MPH in 10 seconds, accelerating at 0.2 MPH/sec, or a little less than .01 G's.

    Furthermore, the bigger you are, the smaller Earth is in comparison. So obviously you'd feel a lot less gravity as a fantasy mega-giant.

    But there's a third premise I thought of, but have started to second-guess in the past day or so. It goes like this:

    3. Every fluid (i.e., all liquids and gases) would feel 500 times thicker to you than it feels to humans, if you're 3,000 feet tall.

    This one I'm feeling a little less sure about. Would fluids really feel 500 times denser? Would they feel the square root of 500 times denser? Or perhaps not at all denser?

    Here's another big question: if you grew to a certain mega-height, would you be able to flap your arms and swim on the air, due to the "lower" gravity and "thicker" air? (Note that water is 784 times denser than air at sea level.) If so, how tall would you need to be to achieve this feat (with the same proportions and bodily density as a human)? And if not, why not?

    For example, if you watch a Boeing 747 jet take off from an airport runway, it seems to be moving quite slow relative to its huge size as it leaves the ground. But try getting a small aluminum 747 toy replica (1-foot long) to become airborne at the same slow relative speed (i.e., relative to its small size), and it'll be impossible.

    So, does the real 747 "feel" denser air, compared to the little replica? Or are other factors at play, here?

    Next, what about skydiving? If a human freefalls with his arms and legs spread out perpendicular to the fall, his terminal velocity at low altitude is about 120 MPH. But what if you're a 3,000-foot-tall mega-giant? Would your terminal velocity also be a mere 120 MPH? Would it be the square root of 500 times 120 MPH? Would it be 500 times 120 MPH? Or would it be something entirely different altogether?

    On the other hand, I also have some doubts about premise #3. If, as a mega-giant, your bodily density is the same as a human's, then why would liquids and gases feel any denser to you? And even if you felt 500 times lighter (due to "less" gravity), you'd still feel just as massive. Your mass would be 500-cubed times a human's. And likewise, so would your physical strength.

    And if you flapped your arms to try to "swim on the air," your arms would push off against 500-cubed times as much air per second, compared to a human moving his arms. But since you're also just as many times more massive, this would cancel out the effect, wouldn't it?

    Ahh,...so confusing!

    But at least there are other things I can be certain about.

    The molecular structure of your bodily organs would need to be completely different from that of humans, or else it would instantly collapse. Perhaps your bones and teeth would be made of carbon nanotubes, or something even stronger. Your skin would be structured differently as well, otherwise it would be scratched and cut too easily.

    And what about the normal people's weapons? If a bullet from a gun travels at 1,000 MPH, this would seem like a mere 2 MPH to a mega-giant. This wouldn't even cut you, and probably would bounce right off. The ammunition would have to contain explosives to inflict any harm (such as grenade guns). To severely injure or kill you, humans would need very large bombs or nukes.

    But if you, as a giant, clapped your hands together at 1,000 MPH (2 MPH from your perspective), there'd be so much kinetic energy released that it'd cause an explosion. (k = 0.5mv^2) Perhaps, for the story's sake, this little physics reality can be ignored! (Ha)

    Anyway, as an occasional fan of these kinds of stories and comics, I've been wondering about this stuff for awhile, and would enormously appreciate it if any of you physics whizzes could give me some answers to these colossal questions!
  2. jcsd
  3. Sep 21, 2013 #2


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    It would feel like instant death. Your legs would be totally crushed by your weight and basically you would turn into a blob of flesh and bones spread out over the landscape.

    The human frame is not scalable very much beyond current size in its existing form. At only 4 times the current average height (and thus 16 times the current weight) you'd need legs like tree trunks, MUCH bigger proportionally than what is normal for humans.
  4. Sep 21, 2013 #3


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    Size of the animal that can survive is one of things researched by biophysics.

    I am afraid most of the things you wrote are wrong, somehow you managed to get every possible effect the other way around. Main problem is with scaling - something that is twice as large in terms of linear size has four times much larger surface (surface grows with a size squared - 22) and weights eight times as much (volume and mass grow with cube of teh size, 23). So no, for th egian 500 times the size of a human the "gravity" won't be 500 times lower, if anything, you can think about it as being 5003=125000000 times higher.

    Not that "gravity" means much in this context.
  5. Sep 21, 2013 #4
    Well, I'm starting to consider some other aspects, now.

    The main one is this: comparing a toddler tripping and falling onto the floor, versus an adult. The toddler falls a lot faster, relative to his small size. But it doesn't hurt him at all, since he has such small mass and weight. The adult falls "slower" -- relative to his adult size, but gets hurt because of his larger weight and mass.

    In elementary school, I remember jumping sometimes from the top of the playground equipment from 9 feet up, onto the gravel below. It was quite fun, and didn't hurt me at all. The teachers sure got scared as hell when they saw me do it, though!

    But if an adult tried the same thing, it'd probably hurt a lot. Even though he'd fall "slower" and "less far down" relative to his adult size (compared to a kid), the adult would probably get hurt, due to his extra mass and weight.

    As a child, I also saw the movie Honey, I Shrunk the Kids. I guess if you got shrunk down to the size of an ant (with the same proportions and density as a human), then you and everything around you would seem to fall incredibly fast, relative to your size. But in spite of that, I guess you'd feel incredibly lightweight, wouldn't you? You wouldn't have hardly any mass or weight. In fact, perhaps you could fall from the kitchen counter onto the floor below (which would be several hundred times your height), and even though you'd fall insanely fast, relatively speaking, you might not get hurt at all, and would just walk away. After all, this is what a tiny mouse does, right?

    Likewise, what if you're a 3,000-foot-tall mega-giant (again, with the same proportions and density as a human), and you fall from a 3,000-foot cliff? Even though the cliff is the same height as you, and although you'd fall very, very slowly (compared to your colossal size), then unless your body were made of carbon nanotubes or some incredibly strong fantasy material, it'd be instant death and collapse the moment you hit the ground.

    So, as a mega-giant, even though you and everything around you would seem to fall very slowly, I guess you'd feel really heavy, right? But again, in these fictional tales, you might not feel so "heavy" if you're made of ultra-strong fantasy material, along with amazingly-strong fantasy muscles (with normal human proportions) that overcome your gargantuan massiveness. (Ha)

    Anyway, am I starting to get things right, now, or am I still way off base?

    But nonetheless, in my first post, can anyone answer my questions about "premise #3" and aerodynamics / fluid density? Why does a real 747 airplane become airborne at such a slow speed -- relative to its huge size -- while a 1-foot-long 747 toy replica made of the same materials would have to go really fast compared to its small size to lift off? Does the real 747 "feel" thicker air than the replica feels, or are other factors at play, here?

    And how about a mega-giant's terminal velocity while skydiving at low altitude, compared to a human? How would this compare? Would a mega-giant "feel" denser air than a human, or not?

    Any ideas, answers, and critiques would be soundly appreciated!
  6. Sep 22, 2013 #5


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    Given that you continue to talk about a

    no, I'd say you still don't get it at all.

    You posit an utterly ridiculous impossibility and then ask questions about it.

    If you start with a false premise, ANY conclusion you reach is logically true, so just make up whatever answers you like.
  7. Sep 22, 2013 #6
    Then what's the point of science fiction, or any fantasy fiction for that matter, where people have special powers, etc.?

    There's a section of this forum dedicated to "science fiction writing," to help people add realistic attributes to their sci-fi / fantasy stories. Although I'm not interested in writing fiction, I'd like to understand some physics in order to separate the realism and fantasy elements in my mind better about some of these stories.

    It'd help answer some questions such as, "What gives a mega-giant the special power to be able to walk around (or even exist at all) without instant death and collapse?"

    Answer: a body with a fictional molecular structure.

    Another example: "What gives Doc Brown the ability to time travel in Back to the Future?"

    Answer: a fictional device called the "flux capacitor."

    Fantasy can be quite fun sometimes, but it helps to add some realistic elements to the story to create a little credibility. Otherwise, too many audience members will start rolling their eyes.
  8. Sep 22, 2013 #7


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    True, but also remember that a toddler is something like 1-2 feet off the ground, at best. An adult, especially our head, is 5-6 feet off the ground. We reach a higher velocity before impacting the ground compared to a child because of this.

    Well, other than already being dead because of reasons already stated, sure.

    You wouldn't feel anything, you'd be dead. And if your body was designed to handle such proportions, then you'd probably feel normal. Attempting to take our perspective at our scale and move it to other scales will not work.

    What you're trying to do is take the way we perceive things on our scale and simply move them to another scale. Since we can't become 3,000 ft giants or 1 mm ants, it's extremely difficult to say what the world would "feel" like at those scales. There's a whole mess of things to think about. For example, I recently read something that said that small animals may "experience" time faster than we do since their nervous systems are much much smaller and signals don't have to travel as far. (Or something like that I think) They are literally able to think and perceive the world at a rate that we would consider faster than normal. But to them, that's normal and we are slow.

    It's a bad idea to talk about "feeling" things. That's not something that anyone here can throw a measurable unit at, so you aren't going to get any answers. Simply put, the planes take off when their airspeed lets them generate enough lift to overcome their weight. I don't know how they scale, as I haven't done the math.

    To explore the possibilities that people have once they have their powers. Rarely does an author expand on how it is possible their powers work with any real technical detail. When you get right down to it, almost every power is simply impossible and attempting to justify it with real world physics won't work because it defies those very laws to begin with.
  9. Sep 22, 2013 #8
    Wow! Very interesting point. I'll have to ponder that one. Thanks!
  10. Sep 22, 2013 #9


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    Note that that it is highly unlikely you would think any quicker if you were shrunk down to that size.
  11. Sep 23, 2013 #10
    Alright, guys, I think I've gotten this "giant fantasy physics" stuff just about all figured out. Here's what I think:

    A. The taller you are, the slower everything falls (relative to your tall height), so you'd feel less gravity. The shorter you are, the faster everything falls (relative to your short height), so you'd feel more gravity. Notice that I'm not talking about mass, weight, or strength -- just gravity.

    B. How heavy you'd feel at different heights and sizes all depends on your physical strength relative to your weight. If you're really strong compared to your weight, you'd feel really light. If you're weak relative to your weight, you'd feel heavy. Simple as that.

    C. If you have the same proportions and density as a human, but are a lot taller, then you'd need the magnitude taller you are to the 4th power times as much physical strength to maintain your proportions for that "apparent" gravity. If you're twice as tall as a human, for example, then you'd weigh 8 times as much, you'd be 16 times stronger, and would feel half as heavy. You could go to a planet with twice the gravity, and feel the same as a human feels on Earth.

    Likewise, if you're 500 times taller, then you'd weigh 500^3 (125 million) times as much, you'd be 500^4 (62.5 billion) times stronger, and would feel 1/500th as heavy. You could go to a fictional planet with 500 times Earth's gravity, and feel the same as humans do here.

    (Obviously, you'd need a body with a really cool fantasy-fictional molecular structure to achieve this awesome feat!) Ha (Otherwise, you'd totally collapse and die.)

    D. The denser your body is, the less dense everything else feels. The less dense you are, the denser everything else feels. If you change your size but keep the same density, then everything else's density feels the same as it did before. Simple.

    E. When skydiving at low altitude as a mega-giant, your terminal velocity compared to a human's would be the square root of your magnitude taller, times the human's terminal velocity. (This Wikipedia page can help to understand this: http://en.wikipedia.org/wiki/Terminal_velocity

    A human's terminal velocity with his arms and legs spread out perpendicular to the fall is 122 MPH. If you're 100 times taller, then your terminal velocity would be 10 times that, or 1,220 MPH. If you're 500 times taller, then it would be the square root of 500 (i.e., about 22) times that, or 2,728 MPH. To you -- the mega-giant, this would only feel like roughly 5.5 MPH, or 22 times slower relative to your height, compared to a human! You would feel 1/500th the gravity, but yet, due to your extra mass, your terminal velocity (in relative terms) would be a "whopping" 1/22nd of what a human "feels." In absolute terms, yours (the mega-giant's) would be 22 times faster than the human's.

    And this is all while feeling the same apparent density of air.

    F. Here's another example: comparing a commercial jetliner with a 100-foot wingspan with a perfectly-scaled toy replica made of the same materials with a 1-foot wingspan. Correct me if I'm wrong about this, but I'll make a little assumption here: the real jet must go 150 MPH to become airborne, while the toy replica needs to go 15 MPH to do the same. Because they both have the same density, the outside air thickness "feels" the same to each of them. What feels different? The gravity. The real jet feels 1/100th the gravity the toy feels! (Again, I'm not talking about mass, weight, or strength -- just gravity. Every object around it falls 100 times slower compared to its size, versus the toy replica's experience.)

    But due to the real jet's extra mass, it still needs to travel 1/10th as fast (relative to its large size) to take off.

    Likewise, the toy replica feels 100 times the gravity, but only must travel 10 times as fast (relative to its small size) to lift off, due to its tiny mass.

    Amazing, huh!

    G. Last point for now: unfortunately, it would be absolutely, completely impossible for you as a mega-giant to "swim on the air," no matter how tall you are. Because your proportions and density remain the same, your extra mass will always cancel out the effect of the extra force your bigger arms exert on the air. In Newton's Second Law of Motion, F = ma, or F/m = a. As you become taller and taller, "F" and "m" will always increase proportionally by the same magnitude, offsetting each other.

    But then you might ask, "But what if you're 500 times taller and feel 1/500th the gravity, and also feel 1/500th as heavy due to your super-duper kickass fantasy strength with the same apparent air density? Since water is 784 times as dense as air at sea level, wouldn't this be enough for you to barely 'swim on the air' a teeny-tiny bit? It might not be much, but wouldn't it be a little something?"

    The answer: Nope. Not at all. Zero. You must recall that, due to your extra mass, your skydiving terminal velocity (in absolute terms) is 22 times that of a human's. Although the air feels just as thick to you, you're 22 times more resistant to it because of your extra mass. And the taller you get, this resistance increases logarithmically as a square root of your magnitude taller.

    Hahahahaha,........OK...........Any questions? :)
  12. Sep 23, 2013 #11


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    Nothing you've said makes a lick of sense at all. How can you calculate what someone "feels" when it's based on perception, not on physics?

    Also, your calculations for the airplane are off. When going down in size by 100 to 1 ratio, your plane is going to weigh something like 1,000 or 10,000 times less at least. Otherwise your model airplane is going to weigh something around 100 pounds. And I don't know what you mean by saying it feels 100 times the gravity. It weighs less and has less stress on its components. It may help if you used another term other than "feels".
  13. Sep 23, 2013 #12


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    Won't hurt if you will start by defining what "gravity" is intended to mean.
  14. Sep 23, 2013 #13
    The difference in mass would be 1,000,000 : 1, wouldn't it? (100^3 : 1) Same proportions, same materials, etc. Maybe the model airplane weighs 0.1 pounds or so. Or, maybe I'm a little off on the weight.

    By "gravity" I mean in a relative sense; not in an absolute. I'm saying that, relative to the model plane's size, everything around it (without wind resistance) falls down at 100 times the acceleration, compared to the scale and scope of the real plane. By "feels," this term is a little hard for me to explain. I mean, in terms of motion in a relative sense, compared to something else, it reacts to the world in a certain way. But yes, the replica obviously weighs less and has less stress on its components; I'm not arguing against that.

    As you said, I'm trying to take the scale of one object, and move it to a different scale while trying to make sense of the differences in the world around it. It's a fascinating subject to me, at least. It's something that giant-themed (or shrunken-themed) stories try to explore. Take Gulliver's Travels, for example.
  15. Sep 23, 2013 #14


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    You can just use the standard terms like force, acceleration, etc. "Feels" doesn't convey anything meaningful when discussing physics. And I think it will make much more sense if you use those terms.

    A larger creature would move slower, relative to its size, for a lot of reasons. Greatly increased mass, increased appendage length puts increased stress on it as the creature attempts to bend and move, etc. When your arm is 300 ft long you can't just whip it around like we can. Sure, you may be able to slap some other giant at 2,000 miles per hour, but it's going to take you a while to accelerate your hand up to that speed.

    The reverse happens when looking at small creatures. When you legs are 2 mm long you can shuffle those puppies along at breakneck speeds, relative to your small size. Even though you're still only going like 1 mph lol.
  16. Sep 23, 2013 #15


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    This is a pure nonsense. If you want to be treated seriously, you have to stick to the real physics, not to handwavy representation of what you feel looks like physics. Behavior of a physical object is described by its mass, acceleration, velocity, forces that act on it and so on, not by some "gravity in a relative sense".
  17. Sep 23, 2013 #16
    In the real world, yes, this is certainly true. I guess it's because larger creatures tend to have a much lower ratio of strength-to-weight (or strength-to-mass) than smaller creatures do, right? So, larger animals tend to be less agile.

    In my last long post above, I mentioned (or implied) something to the effect that you'd probably need the magnitude of height difference to the 4th power times as much strength to enjoy the same agility at larger sizes. For example, if a 6-foot-tall adult wants to be twice the height with the same proportions, density, etc., while being just as agile, he'd need 16 times (i.e., 2^4 times) the bodily and structural strength, which is quite impossible in the real world as we know it. Does this concept sound feasible, or am I just making a wild guess?
  18. Sep 23, 2013 #17
    Just wanted to add: your eyeballs would be amazing telescopes because of the increased aperture.
  19. Sep 24, 2013 #18
    Cool! Maybe you could see the Hubble Deep Field, or something. But you'd need to wear some glasses that convert the radio-wave frequencies to visible light for you to see it. :-)

    I do know this: if you could build an optical microscope at your scale, you could magnify images 500 times more (from your perspective) than humans can from theirs, until the image gets too dark to see. (I think visible violet-colored light wavelengths are about 0.2 microns. You can't see anything smaller than that in visible light.)

    Here's a funny thought: if you were shrunk down to a microscopic size, you couldn't see anything in front of you (in visible light) that's closer than 0.2 microns. You'd need X-ray / gamma-ray vision, or something like that. (Ha)
  20. Sep 24, 2013 #19


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