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Mapping Gravity
overThruster writes: "No, you don't need to drink the water... Gravity is less strong in India--enough so that you weigh almost 1% less there. See BBC story about NASA's gravity map." Here's another story about the mission, and the GRACE home page (or NASA's less-informative page).
I was poking around in all of the sites for a few minutes before I found out that the satellites haven't been launched, and aren't scheduled to go up until Feb 2002. The BBC says it's going to be just a few weeks, but the official site says 97 days.
Interesting note from their site: A secondary experiment that GRACE will perform is to examine how the atmosphere affects signals from the Global Possioning Satellites (GPS). Ahhh, another Slashdot hotbutton! This project just keeps looking better and better the more you check it out.
What's your damage, Heather?
Does this explain why I lost 2 centimetres after moving to Australia five years ago? Went to a medical the other day and the shrinkage was quite unexpected...
Use ISO 8601 dates [YYYY-MM-DD]
Relations between the two countries are tenuous at best. However, both sides are currently working towards some form of temporary ceasefire over Kashmir. The possibilty of the Indian government permitting foreign launch stations on their soil would be counterproductive, and therefore out of the question.
Use ISO 8601 dates [YYYY-MM-DD]
Well, I know Ariane launches rockets from the equator because the force of the spin on the earth is greatest there. I wonder if this gravity map is corrected for actual and measured gravity?
...but you'd weigh more when you got back! It's a proven fact that, among other things, the metabolism slows down in low-gravity environments.
--
erik
THE GOOD HUMOR MAN CAN ONLY BE PUSHED SO FAR
Bart Simpson on chalkboard in episode 2F18
Big deal, you say? Think of the existing physical infrastructure in a city. Now think of a new development that has to tie into the existing water, sewer, storm drainage and roadway systems. If you use GPS and don't take these things into account, you're going to take a chance on sewers that don't drain, storm drainage forming lakes and a general mess (not to mention lawsuits).
Not the typical
Bleh!
You probably hear the 9.8 m/s^2 acceleration due to gravity touted but this is just the net affect across the whole of the globe which is actually very inaccurate when used at specific locations.
Did you know that its actually easier to break the force of gravity ontop of mount everest. I'll show it using the formula:
g = G*(m/r^2)
= ((6.67*10^-11)*(5.98*10^24))/(6.389*10^6)
= 9.77 m/s^2
The value of g also can vary locally on the surface because of the presence of irregularities and rocks of different densities. Such variations in g also known as 'gravity anomilies'. Mineral deposits, for example, have a greater density than surrounding material; because of the greater mass in a given volume g can have a greater value on top of such a deposit then at its sides.
Overall altitude, underground minerals and distance from the equator all play apart in changing the acceleration due to gravity across the globe.
Is it possible that gravity can increase over the lifespan of a planet? I read recently
that 50,000 tons of space dust fall on the earth every day.
Maybe in the time of dinosaurs the earth actually had lighter gravity. Let's see-
50,000 tons of dust X 50 million years = 2,500,000,000,000 (that's 2 trillion tons of dust) that would be enough to effect gravity wouldn't it.
I'm sure my math is off, and that the earth must also lose a fair amount of matter via outgassing etc- But it would explain why such impossible beasts like the brontosaurus were
able to stand under their own weight.
I have no pants and I must scream
The effect of velocity on perception of elapsed time is not linear as far as i know
.85c just to age half as slowly (or mass twice as much or be half as long). The equation is pretty simple; I don't happen to remember it at the moment and am to lazy to Google it.
Correct. As I recall, you have to ramp up to
actually, "moving through time" at all is pretty meaningless, unless you have another time axis to measure against
Why? If I'm moving at all (though the effects only become noticable relativisticly), I'm 'moving through time' at a different rate than someone in an different inertial frame. You don't need a y and z axis to describe differences in motion along x. I get headaches thinking about 4 dimensional geometry.
so moving through time "at the speed of light" is meaningless
Very true. If you move at the speed of light, your perception of the passage of time drops to zero and the life of the universe passes by you in no time. Literally. But since accelerating a body to that speed would require an infinite amount of energy (which I had once, but misplaced), it's not something I feel I need to worry about.
I've always been fascinated by the potential loophole here. You can go slower than light (everything we see) or you can go faster (tachyons?). The only thing actually forbidden is attaining that exact velocity. So figure out a way to jump from one speed to another without going through the intervening velocities (an easy task, right?) and you're golden.
Dyolf Knip
Back in 1978, Arthur C. Clarke ended his book The View from Serendip by writing about a gravitational anomaly which was found off the coast of Sri Lanka (formerly Ceylon) -- the small island near India where he lives.
I am able to visit my favorite spot (Chapter 13) for only a few days a year. But now, quite unexpectedly -- and literally since I wrote the preceding paragraph! -- Serendipity has struck again. While researching a totally different subject, I've discovered a good reason for spending more time on the south coast.
It concerns the greak Sanskrit epic, the Ramayana. In this 2,200-year-old poem, the demon-king Ravanna kidnaps Sita, wife of Rama, and takes her to his island stronghold of Ceylon. Needless to say, she is ultimately released, after aerial battles involving what look suspiciously like atomic weapons and laser beams.
To heal the wounded, the heroic monkey-general Hanuman is later sent back to India to fetch a medicinal herb found only in the Himalayas. Unfortunately, when he gets to the right mountain he is unable to identify the herb. No problem; he brings the whole mountain back! However, one piece drops off, on the southern tip of Ceylon. The locals believe this fragment is in fact my favourite bay, for its name in Sinhalese means "there it fell down" (onna watuna).
There it fell down. Place names usually have a meaning, though it is often lost in the mists of time. Did something really fall down, centuries or millennia ago, at Unawatuna Bay? A meteorite would be the obvious explanation; it must have been a big one for the legend to have lasted down the ages.
And here's another weird coincidence. Little Unawatuna, believe it or not, is the closest point on dry land to the world's greatest gravitational anomaly, a few hundred kilometres out in the Indian Ocean. On the Goddard Space Flight Center's 3-D map of the Earth's Gravimetric Geoid, that strange phenomenon looks liek a deep pit [1] into which the whole island of Sri Lanka is about to slide.
Let's put two and two together. A few thousand years ago, a huge object of peculiar density plunged into the Indian Ocean, creating a tradition that is remembered to this day. And it's still there, distorting the earth's gravitational field -- Terran Gravitational Anomaly I.
That might make an opening for a pretty good science-fiction movie . . . and an even better ending for this book.
Ayu Bowan.
1. One hundred and ten metres below zero reference on the Goddard model (March & Vincent, 1974).
There's quite a large bulge of ocean that trails the moon around the earth, and a similar bulge diametrically opposite to it. There's a smaller bulge due to sun tides.
The GRACE home page doesn't seem to mention the effects of tides. Doesn't all that moving mass of H2O change the planet's mass distribution enough to mess with gravimetric readings?
(Disclaimer: I am not an earth scientist.)