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Old 05-04-2011, 12:26 PM   #1
habbakuk87
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Default Gravity and Height of a Person

Me and my pals had a discussion on how gravity affects height of people on earth. It seems to me that although the earth's mass is not uniformly distributed the gravitational force it exerts is uniform enough that it doesn't have any bearing on the height of a person, with genetics and nutrition being the only factor's. Well, they had other thoughts, what do you guys think?
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Old 05-04-2011, 02:25 PM   #2
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Of course it has an effect on the height of human bodies. It is a compressive force. What does the uniformity of the force have to do with anything? You'd certainly be taller if you were in freefall, because there would be no compressive loading.

EDIT: Oh, I misunderstood your question. You mean depending on where you are from geographically on the Earth. Nevermind.
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Old 05-04-2011, 02:54 PM   #3
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Gravity difference between 5'8 and 6'2 is so minimal, youd never ever notice. Gravity does vary everywhere based on lots of variables, but were talking like .00000000000001 lbs of extra load.
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Old 05-04-2011, 04:28 PM   #4
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Quote:
Originally Posted by Farmer View Post
Of course it has an effect on the height of human bodies. It is a compressive force. What does the uniformity of the force have to do with anything? You'd certainly be taller if you were in freefall, because there would be no compressive loading.

EDIT: Oh, I misunderstood your question. You mean depending on where you are from geographically on the Earth. Nevermind.
Yeah, I wasn't sure where the subject was going either. As soccerman mentioned, gravity isn't exactly 1.0G everywhere on Earth, but it's close enough to not matter.

On some other planet, you might see significant differences if G was significantly different. For terrestrial creatures anyway, aquatic creatures maybe not so much.
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Old 05-04-2011, 05:13 PM   #5
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Apparently some people did some analysis of the gravitational variance of the earth as relates to ski jumping and found that it can make a difference of something like 1 cm or so on the length of a jump.
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Old 05-04-2011, 07:36 PM   #6
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http://news.nationalgeographic.com/n...-nasa-science/

The highs and lows vary by 100 trillionth of "standard earth gravity" (.00000000000001).
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Old 05-05-2011, 08:41 AM   #7
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Quote:
Originally Posted by habbakuk87 View Post
It seems to me that although the earth's mass is not uniformly distributed the gravitational force it exerts is uniform enough that it doesn't have any noticeable bearing on the height of a person...
i fixed your initial statement so that it is both correct AND answers your question. in other words, the factors that cause earth's gravitational force to be unevenly distributed about the surface (elevation, latitude and the earth's rotation, etc.) will also cause slight variations in one's height if he/she travels to different locations on the globe with differing gravitational forces. will you be able to measure it with a tape measure/yard stick? no...heck, a micrometer wouldn't even be precision enough to measure a height difference. but in theory, a slight increase or decrease in the gravitational force at your location will result in slight compression/decompression of the disks in your spine, and thus result in a slight increase/decrease in your height. it may not be measurable, but the change in height most certainly exists despite being arbitrary. as Soccerman06 pointed out, the variations in the highs and lows of earth's gravity are so incredibly small that an instrument with the ability to measure equally incredibly small distance increments would be needed to detect such a small change in one's height.
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Old 05-05-2011, 10:28 AM   #8
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Well if it isn't noticeable then at least in this case we can say it doesn't matter at all.
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Old 05-05-2011, 10:39 AM   #9
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Originally Posted by habbakuk87 View Post
Well if it isn't noticeable then at least in this case we can say it doesn't matter at all.
that is correct - for all intents and purposes it does not matter since such a difference in height would be arbitrarily small and would make no real-world impact...i just figured you wanted an exact answer, and not just a "close enough" answer...
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Old 05-05-2011, 02:06 PM   #10
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You might enjoy this MIT ocw lecture. The full lecture starts with basic stuff about units and measurements, but at around 11m 15s into the lecture he gets into a scaling argument about size given the strength of bones and how much bigger they have to be radially to support larger creatures.

It's a tangent from what you're talking about here, but it's close enough that you might be interested anyways.
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Old 05-05-2011, 04:49 PM   #11
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Its an old engineering puzzle. If you take a steel bridge and double its size in every dimension it will collapse under its own weight. The problem is that the weight of the bridge goes up by the square, while its strength merely doubles. The bridge will double in strength, but it weights 8 times more.

As a result basketball players like 7' 6" Yo Ming weigh over 300 lbs and have to be very careful not to sprain their ankles and break their bones. The tallest person ever recorded was Robert Pershing who at 8' 11'' weighed 485 lbs. The tallest hominids ever are thought to been possibly 10' and weighed 1,000 lbs.
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Old 05-06-2011, 09:18 AM   #12
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@sunny129:Your answer is great, it's just that I was saying the same exact line to them before I posted here.

@Ghiedo: Will check out that video.
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Old 05-14-2011, 06:54 PM   #13
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Old 05-14-2011, 07:08 PM   #14
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The magnitude of the force due to gravity has an effect on the height of the human race - given a much stronger gravity, I would imagine species would tend to be shorter, and opposite for weaker gravity. However, the variation between the different environments in which humans inhabit is negligible - a few kilometers at most. This is in comparison to the 6000-odd kilometer radius of the Earth - if that's what you mean. If you mean the difference between a tall person and a short person, that is even less. Genetic variation and environmental pressures are far more significant.

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Its an old engineering puzzle. If you take a steel bridge and double its size in every dimension it will collapse under its own weight. The problem is that the weight of the bridge goes up by the square, while its strength merely doubles. The bridge will double in strength, but it weights 8 times more.
Cube, surely. Not square.
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Old 05-17-2011, 03:24 PM   #15
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I propose a mental experiment. Given your OP, give this scenario a shot.

Consider identical twins where one was huge eater and chronically overweight by 200% of normal while the other twin was a light eater and chronically underweight by 20% would have a measurable difference in height once they reached adulthood?

If you are argueing purely on the compressive force of gravity leading to noticeable variations in height, the compressive force of the additional weight on the first twin will be exponentially larger force compared to a slight gravitational deviation of twins with identical weight.
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Old 05-17-2011, 04:36 PM   #16
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I propose a mental experiment. Given your OP, give this scenario a shot.

Consider identical twins where one was huge eater and chronically overweight by 200% of normal while the other twin was a light eater and chronically underweight by 20% would have a measurable difference in height once they reached adulthood?

If you are argueing purely on the compressive force of gravity leading to noticeable variations in height, the compressive force of the additional weight on the first twin will be exponentially larger force compared to a slight gravitational deviation of twins with identical weight.
Actually, I think you didn't really argue anything. The compressive force *is* the gravitational force, you know, Newton's 3rd law.

What I think the OP meant would be if you took identical twins and geographically separated them, one in a region of "strong" gravity and one in "weak" gravity and then check their heights.

I agree with Mr. Pedantic, there are other much stronger effects that determine a persons height. Now, the average of the species? How about the average of the species which have been geographically separated in a region with significantly different gravity?
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Old 05-17-2011, 04:52 PM   #17
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LOL, I mixed up the OP and Farmer's response in a single post mashup.
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Old 05-28-2011, 12:55 PM   #18
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The tallest person ever recorded was Robert Pershing who at 8' 11'' weighed 485 lbs. The tallest hominids ever are thought to been possibly 10' and weighed 1,000 lbs.
His full name's Robert Pershing Wadlow. Also, the tallest hominids ever are humans. You're thinking of Gigantopithecus, which was a hominoid. I'm not merely being a pedant - Gigantopithecus was a quadruped, not a biped, so when it moved it was no taller than a person. Gravity also affects quadrupeds differently than bipeds, at least in terms of how the two basic body types adapt to gravity's effects.
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Old 05-28-2011, 04:37 PM   #19
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His full name's Robert Pershing Wadlow. Also, the tallest hominids ever are humans. You're thinking of Gigantopithecus, which was a hominoid. I'm not merely being a pedant - Gigantopithecus was a quadruped, not a biped, so when it moved it was no taller than a person. Gravity also affects quadrupeds differently than bipeds, at least in terms of how the two basic body types adapt to gravity's effects.
Well, there is one thing you forgot to point out.
The gigantopithecus moved on all fours not because of the gravity difference between standing up and walking around on hands and feet, but because of the weight distribution reducing the strain. IIRC for some animals, there is also the problem of power distribution. They could never produce the speeds they manage on 2 legs. Also because the "lumbar" part of the spine is used as a spring(compressing curve and then elongating reducing the curve) during movement. This would be of no use when walking around on 2 legs.

EDIT:
Forgot to mention that humans are really awkward because of being bipeds. Maybe the environment must have been lot's of snow or cold water that made walking as a biped a necessity for the ancestors of humans. This way, the reduction of body temperature can be kept better under control. If only your legs are cold, it is a big difference when compared with the rump and the head.
There are some theories that the ancestors of humans came to existence near places with a lot of water.
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Old 05-29-2011, 06:17 AM   #20
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Being bipedal conserves energy and helps prevent overheating. Humans have very little hair, mostly on the top of their heads, an enormous number of sweat glands, and huge lungs for our size. This allows us to literally run after our prey all day long in the heat and dust of the African plains and literally run them into the ground from heat exhaustion.

Some tribes still hunt this way and it is a uniquely human hunting style and ability. Being able to sprint fairly fast and accurately throw a spear or swing a club while running make this hunting style formidable. While other predators would quickly tire and overheat, we can be relentless. One of the more obvious drawbacks is that probably half of all people have back problems and a large percentage have knee and other joint problems.

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Old 05-29-2011, 10:16 AM   #21
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Being bipedal conserves energy and helps prevent overheating. Humans have very little hair, mostly on the top of their heads, an enormous number of sweat glands, and huge lungs for our size. This allows us to literally run after our prey all day long in the heat and dust of the African plains and literally run them into the ground from heat exhaustion.
This theory is nice. But i do not think it is the entire answer. We do not have provisions to store huge amounts of water inside our body. We would burn up quickly if we would run for days without rest and water in the hot plains of Africa. When thinking of temperature, it makes sense that the brain is at the highest point of the body since we uses a lot of energy and also the brain dissipates a lot of heat. The temperature of the ground is higher then the air above it. Everybody knows it is harder to think in a hot climate when compared to a cold climate. Why do we have sweat glands and huge lungs ? It makes more sense that the environment evolved us into it and that hunting techniques are only part of the puzzle. High altitude mountains. Moving around as we can do is beneficial in a rocky climate where the temperature changes quickly from cold to hot. I always wondered if human ancestors are natural rock climbers instead of tree climbers.

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Some tribes still hunt this way and it is a uniquely human hunting style and ability. Being able to sprint fairly fast and accurately throw a spear or swing a club while running make this hunting style formidable. While other predators would quickly tire and overheat, we can be relentless. One of the more obvious drawbacks is that probably half of all people have back problems and a large percentage have knee and other joint problems.
We know this hunting technique works to a degree, but it does not proof that hunting is the primary reason. I do believe that we are hunters for meat and gatherers of fruits and vegetables. The human digestive system gives me this idea. It is very versatile. I always wonder if we are the only one with such a versatile digestive system. Most animals have an digestive system optimized for a certain type of food range. With the speed new tissue is produced, it makes sense that our bowels could evolutionary adapt faster. Especially since we are dependent on the bacteria and fungi that live inside out bowls.

Back problems and joint problems yes. The evolutionary solution is to have children young. We need an improved spine and joints.

Another reason to live in the cold is maybe a conscious reason to be free of insects plagues and cold blooded animals such as venomous snakes. It would make sense. And the most fertile lands are always to be found near volcanoes.
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Old 05-29-2011, 10:31 AM   #22
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It does not proof much but it is interesting nevertheless :

http://news.discovery.com/archaeolog...ettlement.html

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The world's oldest known high-altitude human settlements, dating back up to 49,000 years, have been found sealed in volcanic ash in Papua New Guinea mountains, archaeologists said Friday.

Researchers have unearthed the remains of about six camps, including fragments of stone tools and food, in an area near the town of Kokoda, said an archaeologist on the team, Andrew Fairbairn.

"What we've got there are basically a series of campsites, that's what they look like anyway. The remains of fires, stone tools, that kind of thing, on ridgetops," the University of Queensland academic told AFP. "It's not like a village or anything like that, they are these campsite areas that have been repeatedly used."

Fairbairn said the settlements are at about 2,000 meters (6,600 feet) and believed to be the oldest evidence of our human ancestors, Homo sapiens, inhabiting a high-altitude environment.

"For Homo sapiens, this is the earliest for us, for modern humans," he said. "The nearest after this is round about 30,000 years ago in Tibet, and there's some in the Ethiopian highlands at around about the same type of age."

Fairbairn said he had been shocked to discover the age of the finds, using radio carbon dating, because this suggested humans had been living in the cold, wet and inhospitable highlands at the height of the last Ice Age.

"We didn't expect to find anything of that early age," he said.

The findings, published in the journal Science, suggest that the prehistoric highlanders of Papua New Guinea's Ivane Valley in the Owen Stanley Range Mountain made stone tools, hunted small animals and ate yams and nuts.

But why they chose to dwell in the harsh conditions of the highlands, where temperatures would have dipped below freezing, rather than remain in the warmer coastal areas, remains a mystery.

"Papua New Guinea's mountains have long held surprises for the scientific community and here is another one -- maybe they were the home of Homo sapiens' earliest mountaineers," Fairbairn said.
When it is very cold, i can imagine that hot springs near a volcano can be favored a lot.

I forgot to mention that the ice ages may have played an important part.
It is most likely that homo sapiens came to be because of the cold weather. Since it seems we are able to adapt to cold easier then we are able to adapt to hot temperatures (meaning we can perform large amounts of work without burning up and having a heat stroke) The problem here is that there is not much food in too cold environments except for the water where fish can be found.
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Old 05-29-2011, 10:49 AM   #23
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I imagine if we evolved on a world that was more oblate what's being discussed would be possible. Imagine the differences in life in a single ecosphere where the gravity at the poles is >60x the gravity at the equator. You'd have a situation where life would develop so radically different depending on where it is that you could travel (in theory) from your point of origin to another on the planet and it would truly be like visiting an alien planet.

There was a hard scifi book about this released awhile back that postulated this very scenario. I can't think of it atm though.

edit Ah, remember, it's 'Mission of Gravity'.
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Old 05-29-2011, 10:50 AM   #24
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edit - double post
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Old 05-29-2011, 11:26 PM   #25
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I forgot to mention that the ice ages may have played an important part.
It is most likely that homo sapiens came to be because of the cold weather. Since it seems we are able to adapt to cold easier then we are able to adapt to hot temperatures (meaning we can perform large amounts of work without burning up and having a heat stroke) The problem here is that there is not much food in too cold environments except for the water where fish can be found. [/I]
The basic physiology of hominids predates the last ice age. We were standing upright and using stone tools and fire when our brains were still 1/3 to 1/2 their current size. However, what has puzzled anthropologists is that they used the same primitive tools for millions of years. The popular explanation was that the explosive growth in technology after the last ice age was due to the development of complex language, however, more recent findings have shown that some isolated hominid cultures had advanced technology and even art long before the ice age.

I think the research of the Yerkes Institute sheds some light on at least one possible explanation. The researchers noticed that the apes they studied had no innate interest in teaching or being taught. Even such simple human behaviors as a toddler pointing at something of interest was absent and the apes were either lucky enough to witness or had to reinvent the wheel every time.

In one experiment a chimp that had been taught sign language was abandoned with a wild troop. After struggling for months to teach the others sign language it finally abandoned all hope. These are not stupid animals, quite the contrary, they have shown a capacity for even abstract thought. What was missing was any culture or innate desire to teach and be taught. Other animals might instinctively teach basic survival skills to their young, but anything beyond that is of no interest to them. Thus our command of an upright stance, opposable thumb, language, tools, and art may have been a very social affair from the start and influenced as much by our social nature as by environment.

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