Earth's spin/gravity, effects on humans

[l0rca]

I'm having an argument with my friend. He tells me he has this 'theory' that the main reason humans are living longer is because the earth is spinning slower and slower, 'therefore there's less gravity,' and the lesser gravity provides less stress to our bodies, and we live longer.

I think it's laughably rediculous, but he won't back down from his point, and claims it can't be disproven. Like everyone else in the military, he won't listen to reasoning. So I ask what sort of sources may disprove his point and provide the most accuracy to the topic.

What is the rate of deceleration of the earth? What are its effects on gravity? What does this have to do with the longetivity of humans?

[Terry]

Reducing the rate of rotation of the earth does not change its gravitational field. However, if the earth rotates more slowly, then the accelleration required to keep us stuck to the ground gets smaller. Therefore we appear to weigh slightly more. The earth's rotation is slowing down, due to tidal drag. So far as I can tell this has nothing what so ever to do with the longevity of humans.

Hope this helps...

[Dark Jaguar]

Just ask for evidence for his point and point out that the earth's spin is not what generates gravity, it's MASS does that. If the planet wasn't spinning at all, we'd be just as heavy. Try the rotational poles if you want to experience that yourself. It's about as spinless as you can get, or at least you won't feel any force tossing you off the planet.

But hey, you want silly stuff? Try talking to someone convinced the moon "has no gravity because it has no air". Pointing out gravity is not a function of atmosphere, but rather it's the other way around, is kinda tough... At least this fellow was open minded enough to accept correction, and when I pointed out that the moon does in fact have gravity, just less of it, and pointed to the fact that people on the moon in all that footage were being pulled down when they hopped along and didn't just hop straight into the void, well he accepted that well enough. Very strange confusion but in retrospect he's certainly one of the more sensible people I've met. I much prefer someone who has outrageous ideas about the world but is ready and willing to be corrected or find information counter to that to someone who has only mildy incorrect ideas but is completely unwilling to change their mind no matter what the evidence or lack of it may say.

[Yllanes]

The centrifugal force due to the rotation diminishes the effective gravity. Earth's gravity is strongest at the poles, where there is no acceleration and weakest at the Equator. The force goes roughly as

9.83 - 0.34 cos2a (m·s-2)

where a is the latitude. I say 'roughly' because the asphericity of the planet has a comparable effect (which reinforces this).

So, ask him if people live longer on the Equator...

[Jimbo07]

So, ask him if people live longer on the Equator...

Controlling for sunshine and polar bear attacks... :D

[l0rca]

Thank you guys, but are there any educational URLs you know of that may help?

[steve s]

Try talking to someone convinced the moon "has no gravity because it has no air". Pointing out gravity is not a function of atmosphere, but rather it's the other way around, is kinda tough...

In the movie Armageddon, there's a scene when they first land on the asteroid. When they're inside the craft everyone is walking around normally as if there's 1g. But as soon as they step outside the shuttle, everyone starts hopping along in slow motion. Apparently shuttlecraft have a great deal of influence over gravity.

Steve S.

[Art Vandelay]

In the movie Armageddon, there's a scene when they first land on the asteroid. When they're inside the craft everyone is walking around normally as if there's 1g. But as soon as they step outside the shuttle, everyone starts hopping along in slow motion. Apparently shuttlecraft have a great deal of influence over gravity.

Steve S.Magnetic boots?

I'm not convinced that lower gravity is healthier. Certainly there is a point at which lower gravity is clearly worse; people who spend several months in space have serious health issues. Higher gravity would mean one would get more exercise, right?

[HappyCat]

Here is an article if you need an educational link from the Internet:
http://www.newton.dep.anl.gov/askasci/phy99/phy99x82.htm

You are correct though, the spin of the Earth in no way affects how much gravitational pull the Earth has. I am not sure what effect lower gravity would have on human life span. I know when you go into space, the calcium leaves your bones, which makes them and you very weak when you come back to Earth. This is an extreme example though, so I am not sure if it applies to what would happen if gravity were lessened here on Earth. I suppose it would depend on how much you reduced gravity. I would imagine that too much or too little gravity would be unhealthy long term.

[wollery]

The equation for the acceleration due to gravity is;

a=GM/r^2, a is the acceleration, G is a constant, M is the mass of the Earth, r is the distance from the Earth's centre of mass.

Show him that, or find it anywhere on the web, and ask him where rotational speed enters that equation. Then get a weight on a string and swing it around, ask him if the weight is being pulled inwards or pushed outwards by increasing or decreasing the rate of rotation.

[Hindmost]

Wikipedia is just great.

This covers most of the earth slowing down stuff. It is interesting, especially the part where earth's rotation has been increasing a bit since the last ice age. The effect on the length of the day is in milliseconds per century...so, with humans not being around for that long...the effect of the change in the day is nothing. Of course--as stated previously gravity is based on mass.

Intertial effects with the spin of the earth will cause a person to weigh about 0.333 percent less than at the poles. Modern medicine and knowledge of the causes of infections has been the biggest factor in longevity.

http://en.wikipedia.org/wiki/Tidal_acceleration

Tell your friend that general relativity will make you age slower in a strong gravitational field to external observers. Einstein figured that out a long time ago...so, you age faster at the top of a mountain. It will be in nano seconds, but it does happen.

For a quick lesson on gravity. http://en.wikipedia.org/wiki/Gravitation

glenn:boxedin:

[Anacoluthon64]

The way I read the OP is that mercuryturrent's friend seems to be arguing that the Earth's spin produces a centrifugal reaction in bodies, which effectively reduces the force they experience due to gravity. If this is indeed the case, then the argument is back-to-front, since the slowing revolution rate means the centrifugal force reduces over time, and thus the effective g should increase over time, everything else being equal.

The magnitude of the reduction is

dg = R.ω2.cos a,

where R is the Earth's average radius (about 6,270 km), ω is the angular velocity (currently about 7.272 x 10-5 rad/sec), and a is the latitude (equator at 0º, poles at +/-90º). You can calculate the angular velocity from the length T of a full day in hours according to

ω = 2.π/(3,600.T) = 0.001 745/T.

Currently at the equator (where it is largest), the reduction amounts to some 0.033 m/s2, i.e. about 0.33 % of g, which is tiny. By comparison, if the Earth spun twice as fast doing a full revolution in 12 hours, the reduction would be 0.133 m/s2, i.e. about 1.35 % of g, which is still tiny.

A different (and rather more farfetched) take is that the Earth's spin means there's energy of rotation. As this rotation slows, this energy diminishes and, through the Einsteinian mass-energy equivalence, results in an effective reduction in the Earth's mass and a consequent reduction in the strength of g (where g = G.M/R2, M = Earth's mass & R = Earth's radius). This tiny energy change over time is, however, insignificant compared to energy changes brought about by Earth's internal processes, e.g. radioactive decay, or influx of energy, primarily from the sun.

Even more farfetched is if the argument seeks to use results of General Relativity that show how time is affected by a gravitational field. The Earth's gravitational field is far too weak to significantly affect the passage of time.

If the argument is that the strength of Earth's gravitational field depends strongly on our planet's rate of spin, then that is unadulterated nonsense, as pointed out by others in this thread.

As far as people living longer, I think the most powerful argument against this silly gravity idea is that wealthy first world countries (where healthcare and ancillary technologies are readily available) have a significantly higher life expectancy than do poor third world countries. The gravity :D of this difference has a far more prosaic explanation.

'Luthon64

[Harlequin]

I recall seeing, years ago, a chart showing that the increased life expectancy was mostly due to eliminating childhood diseases (i.e. vaccination).

Does anyone have any more information on that? If life expectancy in the US has gone from 60 to 72 in the past 200 years, but 10 years worth of that is from vaccines, it's certainly easier to believe that the rest is just better nutrition (OK, unlikely;) ) and improved medical capabilities.

It also puts more of a limit on the extrapolations that show us living to 300 by the end of this century...

[Yllanes]

I recall seeing, years ago, a chart showing that the increased life expectancy was mostly due to eliminating childhood diseases (i.e. vaccination).

Certainly when we compare life expectancy today to life expectancy in the Middle Ages or Ancient time this is the case. Saying that the average Roman lived only for 20 years is a bit misleading. What really happened was that there was a huge child mortality, but the human body tends to keep on working for a while if it manages to reach adulthood. Hence the fact that many historical characters lived long lives, while life expectancy in their societies was very short. For example, Sophocles lived for about 92 years and even managed to write one of his best plays, Oedipus at Colonus as a nonagenarian; we know it's one of the best because it is one of 8 conserved among some 100+ written. Another could be the sophist Gorgias, who lived to be over 100 years old.

[CP489]

Like everyone else in the military, he won't listen to reasoning.


The stereotyping is unneccessary, this adds nothing to your post, and it's patently false.


CP (USAF)

[Ziggurat]

In the movie Armageddon, there's a scene when they first land on the asteroid. When they're inside the craft everyone is walking around normally as if there's 1g. But as soon as they step outside the shuttle, everyone starts hopping along in slow motion. Apparently shuttlecraft have a great deal of influence over gravity.

Steve S.

That was an unbelievably bad movie, with amazingly terrible science. The asteroid was deflected at the last moment by a nuclear bomb just above the atmosphere, which (considering the inefficiency of a nuke as a propulsion device for an asteroid) would only have been possible if the nuclear bomb released significantly more energy than the kinetic energy of the asteroid. So if the asteroid had much less energy than the nuke, what were they all so worried about?

[gfunkusarelius]

did youir friend have any studies at all to support his ideas? frankly, since he is the one making the claims, it is up to him to provide evidence for it, not for you to find evidence to the contrary. otherwise it essentially amounts to the old "i have a dragon in my garage, disprove it." its not really even worth your time to challenge him if he has no science.

and as others have pointed out, even if some part of his theory (or some more correctly defined version of his theory) had some validity, i very highly doubt that it is the "main" reason for increased life expectancy since there are so many other very clear and defined reasons.

[Cecil]

did youir friend have any studies at all to support his ideas? frankly, since he is the one making the claims, it is up to him to provide evidence for it, not for you to find evidence to the contrary. That's only true if the two people are working together to arrive at the truth.

In this case, his friend is convinced of the truth of a patently false notion, and disabusing him of this belief requires more than just saying "you're wrong".

[Beady]

In this case, his friend is convinced of the truth of a patently false notion, and disabusing him of this belief requires more than just saying "you're wrong".

Actually, saying "Your wrong" constitutes a claim which, itself, needs supporting evidence.

[l0rca]

The stereotyping is unnecessary, this adds nothing to your post, and it's patently false.


CP (USAF)


I too am in the military, so perhaps you can pardon my fun.


did youir friend have any studies at all to support his ideas? frankly, since he is the one making the claims, it is up to him to provide evidence for it, not for you to find evidence to the contrary. otherwise it essentially amounts to the old "I have a dragon in my garage, disprove it." its not really even worth your time to challenge him if he has no science.
-gfunkusarelius

No. Last night, like me, he did research, but he stopped at looking at something that said the earth was slowing its spin. I provided him with a number and example of its slowing, and he thought me ridiculous -- he was sure it was decelerating at a far more dramatic pace.

Of course, then I went into the fact that the only thing about spin that affects gravity is the acceleration differences of the tectonic plates and our core, which affects the geography of the planet more than it does us.

However, if the earth rotates more slowly, then the acceleration required to keep us stuck to the ground gets smaller. Therefore we appear to weigh slightly more.
-Terry

Do you mean that although the spin has no affect on the gravitational field, it has effects on our resistance to gravity, therefore we weight more, and it appears that the gravitational field is growing?

The equation for the acceleration due to gravity is;

a=GM/r^2, a is the acceleration, G is a constant, M is the mass of the Earth, r is the distance from the Earth's centre of mass.

Show him that, or find it anywhere on the web, and ask him where rotational speed enters that equation. Then get a weight on a string and swing it around, ask him if the weight is being pulled inwards or pushed outwards by increasing or decreasing the rate of rotation.
-wollery


Actually, as I was talking, he interrupted me to point that out, but with a bucket of water on a string instead. He insisted that the spin of something affects the earths gravity because of that. I told him all he was doing was creating another gravitational field through acceleration, trying to briefly explain the equivalence principal. I also added that if he doesn't know anything about General Relativity he shouldn't use it to support his argument.

The argument is over now anyway. It's come to the point where he's simply being defiant in light of evidence. In a last act he attempted to bring a group of our friends in on the discussion, to convince them of his 'theory'. I feared that this would turn into an Argumentum ad Populum, considering they very well may not know better than he does, but fortunately there were two Stephen Hawking fans in the crowd, and another that felt nutrition, hygiene, and medicine was a much better explanation. Still, he refuses.

[CP489]

I too am in the military, so perhaps you can pardon my fun.




My bad then.