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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).
No, then it would be cheaper to ship things FROM there, since you get more than a ton per ton. And you could get on the plane with 70 lbs. of stuff, and when you arrive in (wherever) laugh uproariously at the ticket agent, dancing around and saying "ha HA! I have 71 pounds in my bag!"
"If he thinks he can hide and run from the United States and our allies, he's sorely mistaken." Bush on bin Laden
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?
This was Astronomy Picture of the Day last week.
Plenty of depth/background available from there, as always!
"If you create user accounts, by default, they will have an account type of Administrator with no password." KB Q293834
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]
5 lbs, but man, you should really get some exercise. Lay off the Quake for a while. Maybe 1-800-20JENNY can help.
"If he thinks he can hide and run from the United States and our allies, he's sorely mistaken." Bush on bin Laden
Mapping the geoid is one of the most fundamental problems in oceanography. Ocean currents are all basically caused by water running downhill. The problem is that "downhill" in this case is relative to the geoid, which is a bumpy, not-nice surface. With this kind of map, we should be able to map surface currents from space; their velocity, their position, everything you want to know about how the surface currents are moving. This is important for climate studies of global warming, since the ocean currents are one of the main transporters of heat from the equator to the poles. This will allow us to get a much better idea of where the heat in the world is going, and how long it takes to get there, which in turn will give us a better handle on global warming.
Oceanographers have been trying to figure out a way to remove the geoid from their equations for a hundred years. Now we can just measure the damn thing. Crazy.
"The contents of this package are shipped by weight, not volume. Some settling may have occured."
:)
They're consistently defrauding India. Honeycomb's big (yeah yeah yeah) but it's not quite AS big in India? Sue sue sue!
Well, if you had read the article, instead of just looking at the pictures, you would have noticed the paragraph that states:
"Every month during Grace's five-year expected lifetime, we will get a map of the Earth's gravitational field," says Michael Watkins of the American space agency's Jet Propulsion Laboratory.
"If he thinks he can hide and run from the United States and our allies, he's sorely mistaken." Bush on bin Laden
A guy is throwing a ball up into the air and the caption reads "Nasa's Michael Watkins: A new map every month." What does that picture have to do with anything?
He studies gravity, making gravity maps for NASA. Get it? Throwing a ball up, the ball comes down, forces at work.... Ringing any bells?
I thought it was brilliant. One of the funniest publicity photos I've seen in a while, better than the dot-com ones.
What's your damage, Heather?
Hell, in my physics classroom it's about 30% as strong as anywhere else. I proved it myself in a lab last week- it's about 3.2 m/s^2 in our corner of the room!
Strangely enough, it's just about 9.8 up front. I guess the earth is pretty aspherical.
-Toad
--
- It ain't easy, being green.
So if things weigh less in India, wouldn't launching rockets and shuttles from there be easier? A 500,000-pound rocket would only weigh 495,000 in India - not a huge savings overall, but you could reduce fuel consumption and save money or go a bit further on the same amount of fuel. And the location is about as far south as Florida, so that's enough planetary curve for them. Should we expect to see more US companies building launch facilities in SE Asia after this report has been out a while?
== Paul Rickard, Editor of The Microsoft Boycott Campaign ====
Weight != mass, dude. 1 tonne of mass takes just as much energy to move 1 kilometer across the earths surface, whether it exerts 1 "tonne of force" or 0.9 "tonnes of force" due to gravity. Basic physics. UPS hasn't ripped you off (not like they did to this guy, anyway). It's only when you go vertical that you have to counter gravity - and that's when weight becomes significant.
Oh, and the SI unit of force is a Newton (N), which is a kilogram-meter per second squared (k-m/s²). One tonne (1000 kilograms) of mass would exert 9.8 KN (KiloNewtons) of force at mean gravity on the earth. Weight apprears to be the same mass since we use gravity to comapre masses, but they are not the same. As well, in the US and Imperial systems, 1 lb of mass exerts 1 lb of force - just to be confusing.
That concludes tonight's lecture. (My Physics teacher would be so proud. *snif*)
Soko
"Depression is merely anger without enthusiasm." - Anonymous
enough so that you weigh almost 1% less there
Here's a little food for thought though:
"Even a fat bastard on the moon still looks like a fat bastard"
:)
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]
...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
>>As well, in the US and Imperial systems, 1 lb of mass exerts 1 lb of force - just to be confusing.
<<
Actually, in metric land (precisely, in the land of the metre), the kilogram-force (kgf) has been in widespread use, about a century ago. It was more or less equal to the gravity force exerced by earth on a piece of matter with a mass of 1 kg. It took several decades to get rid of that unit (you can still sometimes see indications like "max 2000 kgf" on cranes in old workshops).
Nowadays, low-level mechanics are taught to use the decanewton (daN) as their primary unit of force (be it weight or any other force)... no wonder why !
...the fact that moving at speeds approaching the speed of light will cause you to move faster through time, so that if you left Earth, travelled at near light speeds, and then came back shortly afterwards, 100 years might have elapsed on Earth in what you perceived as about 10 minutes.
I think that physical laws like this have a very significant effect on the lumpiness of the Earth, and therefore, on the variations in gravitational pull.
Imagine that you're running down a square field, from one side to the side parallel to it, and it takes you 10 minutes to run across this field. Ok, now imagine that you're running across the same field, but instead of running "straight," you're running at an angle, so that you're not perpendicular to the edges of the field that you're running from and to. It will take you a bit longer to get to the other side of the field, even though you're running at the same speed, because by going at an angle, you've increased the distance you have to go to get from one edge to the other.
Now suppose we call the field a 2-dimensional surface, like a piece of paper. You could say that the first time you ran across the field, you travelled along one axis, or dimension--let's say the X axis. But on the way back, you ran at an angle, which means that you've gone along two axes, the X and Y axes. But you went the same speed. This means that you have split the same speed across two dimensions.
We say that time is a fourth dimension. Now picture this: No matter what's happening, you're ALWAYS moving through the 4 axes (the three "space" dimensions and the one "time" dimension) at exactly the speed of light. It's just that you're splitting that speed (the speed of light) across some combination of the 4 dimensions. You're doing one of the following:
I think all of these physical laws have a very significant effect on the lumpiness of the Earth, and therefore, on the variations in gravitational pull.
And, of course, the obligatory OH WELL.
Is that why those people stand on their heads over there? You see all of these Hindu guys doing handstands for days and the like... I knew there was I reason I can't do a handstand. Damn that unfair gravity!
Um, this is my sig.
As well, in the US and Imperial systems, 1 lb of mass exerts 1 lb of force
The pound is never a measure of mass, the "imperial" mass unit is the slug.
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
...when you think about it. But that's another topic. You want a demonstration of force, try the weak nuclear force. When you drop a ball of off a building, it accelerates (~9.8M/s/s) but when it encounters a weak nuclear force (the atoms in the 'ground' where it 'hits') it effectively 'stops'
;)
In other words, it's not the fall that kills you, it's that sudden stop at the end
Gravity smavity... let's investigate something interesting
(in all fairness, my buddy's father is a nuclear scientist who holds the current best measurement for Big G, but I still can't believe it's a 'force' per se)
"Whoever would overthrow the liberty of a nation must begin by subduing the freeness of speech."--Benjamin Franklin
That's because Kilograms denote mass, not weight. So the kilos will stay the same, but pounds will change.
Lars T.
To the guy who modded me down from perfect to terrible Karma - Apple haters still suck
Lars T.
To the guy who modded me down from perfect to terrible Karma - Apple haters still suck
Search google for "sandwell chicxulub cretaceous." It'll point you to a gravity map of the crater. I'd give you the link but slashcode keeps mangling it.
As I recall, the debate is between an asteroid/comet impact in the Yucatan vs a violent and prolonged period of volcanic activity in India causing the mass extinctions 65 MYears ago. Both would produce huge amounts of dust and ash and lay waste to whole continents. Problem is, geology can't quite pin down which one caused it. Hell, it could be both that pushed them over the edge, though the timing for that would be rather amazing.
Dyolf Knip
The problem is, and of course the word 'relativity' is supposed to clue you in to this, is that the Earth is also moving away from you at near light speeds. So, 100 years might elapse for you while on Earth they only perceive 10 minutes.
Tricky shit.
Endless arguments over trivial contradictions in books written by ignorant savages to explain thunder in the dark.
Guess what the common English unit for mass is.
Pounds!
If you knew what you were talking about, you..well, wouldn't talk. There is lbm (pounds mass) and lbf (pounds force). So, if the scale were calibrated with a known mass (whether a kilo or a lbm) *at* its location of use, the scale would correctly report mass. In pounds.
So, the force of gravity doesn't matter if the scale is correctly calibrated.
I don't know what differences an asteroid impact would leave, but I do know there is at least one theory for a mass extinction asteroid event on the Indian subcontinent. According to theory though this was a biggie, and the asteroid impact punched through the crust of the earth and released large quantities of magma from the mantle to fill in the crater. The main evidence for the theory anyway, is the observation of massive granite deposits (which forms from cooled lava).
My memory is a bit fuzzy as to which time period and event they were trying to associate it to, but I think it was much before the extinction of the dinosaurs. I'm tempted to say they wanted to connect it with the mass extinction immediately preceeding the age of dinosaurs, but I'm not sure now. Anyway, usually people claim a Yucatan impact site as being the most likely location for the event that may have killed the dinosaurs.
Since I don't have any karma I can't lose it
The worst terrorist attack in recorded history occurred on September 11th, and now we're involved in a WAR against Islam and you people have the gall to be discussing mapping gravity????
Yes, we have the gall.
Ask NAVO (the Naval Oceanographic Office) just how much gall they have, mapping gravity over the surface of the seas! In the Old Days, before nifty toys like Satellite Gravity, we used to grid the earth's field by taking in situ measurements all over; *much* of which was done by oceanographic research vessels
Now, a good portion of that gravity grid was done for nice oceanographic or geologic reasons; if you know the density of the stuff below you, you can get a pretty good guess at the shape and contents of the seafloor below, but curiously, the more sensitive and more accurate gravity meters were owned and operated by the USN.
Why is that? Because a good map of the gravity patterns of the sea floor can help with navigating around it, when you *haven't* the luxuries of GPS or loran or other positioning systems.
Submarines!
Gravity maps done by NAVO ships in the Indian Ocean (which have greater detail and precision than the NASA maps, even if they are much narrower and smaller region of coverage) are quite possibly as we speak, helping guide USN subs in the vicinity, as they prepare for any lurking regional threats.
For a quick glimpse of grav fluctuations in the south pacific, as recorded on a Navy Gravimeter (aboard a civilian research ship) try at the bottom
Anyway, most everyone in the Oceanographic community is really excited about satellite gravity, since its coverage is just about universal (except for the poles) but we still lug out the Bell Aerospace meters (ugly black things) from port to port.
If anyone were interested, I could post descriptions of how some or any of these things work, except this is slashdot and this post will probably end up as (Score:-1, TrollFood)
First, nothing begins if not opening
How does the military deal with changes in the force of gravity due to altitude and location? A 1% change in gravity is a big deal if you are firing an artillery shell at a target over a long distance. I was watching a documentary on the ENIAC computer and it said the computer's primary task was to calculate gunnery tables for the military. Wouldn't all of those carefully calculated tables be useless if the force of gravity changed?
Mea navis aericumbens anguillis abundat
Well, one litre is 0.001 cubic meters, water is water and freezing point is freezing point. I'll leave the rest to somebody with too much time - or somebody with students ;-)
Lars T.
To the guy who modded me down from perfect to terrible Karma - Apple haters still suck
A new gravity map of the Earth suggests that if you want to lose weight you should go to India, where the pull of gravity is slightly less than it is elsewhere on the planet.
Since you weight less, wouldn't you be expending less energy when you move, and therefore get less excercise, and therefore get fatter?
> I thought the English/Imperial unit of mass was the slug, not the pound.
The slug is a unit of mass, with the pound as the corresponding unit of force AND the pound is a unit of mass, with a poundal as the corresponding unit of force. Yes, the Imperial system does suck for science and engineering compared with the metric system.
In practice the pound gets used for both force and mass without too much confusion, just as people talk about their weight in kilograms.
rant
...Gravity is less strong in India...
So *this* explains the Indian Rope Trick!
:-)
It's huge. It's only hidden because it's under water. Check here for pictures of said hole in the ground.
Sorry. Couldn't resist...
I'm trying to teach myself to set people on fire with my mind... Is it hot in here?
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.)
yes, but a ton is 2000 lbs, which makes his comment relavent and yours not.
There are few pseudo-sciences as well entrenched as Astrology. Every once in a while somebody tries to rationalize the effects of Astrology as an actual gravitational effect of the planetary alignments that has a slight but important effect on world affairs and on individual people's destiny. The problem with this is, that there are so many other variations in the Earth's gravitational field that no such effect could get through the background noise. As a geophysicist, I've used measurements of the variations in the local gravitational field to model underground structures, ranging in size from the Rio Grande Rift in New Mexico, to small landfills and service tunnels on the campus of UT Dallas. We never correct for planetary gravity. In fact, when doing gravity measurements in the field, you have to make sure to park the truck a few yards away from where you take your measurement, because an SUV has enough mass to mess up your reading. The mass of Mars, or even Jupiter is very large, but so far away that the SUV a few feet away has several orders of magnitude more influence.
Astrology doesn't work through any physical medium.
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