05-12-2010, 06:28 PM
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Member [03%]
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All right, my question is based off of a very limited knowledge of gravity. I know it travels in waves, and it pulls people downwards at 9.81 meters/second squared.
Any way, I just happened to be watching something on TV about either gravity or obesity when I thought of this idea (which has probably been considered a million times and deemed preposterous): What if there were specific areas one could walk with a stronger gravitational pull? These could be weightloss centers where people could do stuff like they would at an ordinary gym, or just walk around and let gravity help with the muscle building. People could just stay there for a while and work out for half the time they would at a regular gym. Thoughts, anyone?
Last edited by Synamon; 05-17-2010 at 07:27 AM.
Reason: split from "Ask a science or health question"
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 propionaldehyde is offline
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05-12-2010, 06:31 PM
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#2 |
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gravity doesn't "travel", it exerts
and that idea would probably work, though people with weak bodies that weren't already in shape would likely be at high risk of injury in a higher gravity environment |
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ArtistTyrant is offline
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05-12-2010, 06:49 PM
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propionaldehyde is offline
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05-12-2010, 07:23 PM
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Gravity does vary along the Earth's surface, but nobody knows exactly why.
An individual's body does have to work harder under conditions of higher gravity, but the more interesting aspect is that time slows down if the mass of an objective is larger (thus more gravity.)
I'm rather sure your statement is pointless, but would you care to explain further? I'll help ya out.
I'm going to nit pick about the wording you used though I assure you I have a point. To say gravity pulls is to say gravity is a force. First of all there is no proven theory of gravity and some theories do suggest it is a force. However, the most promising theory (because it is so testable) and the one I personally adhere to says that gravity is NOT a force. Simply put, Einstein's General Theory of Relativity says that gravity is the result of space-time fabric that is curved by objects with mass. |
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admittedheretic is offline
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05-12-2010, 07:26 PM
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well lets see who agrees with me about gravity then?
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ArtistTyrant is offline
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05-12-2010, 08:44 PM
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Could this be because some areas of the Earth are more dense than others?
Heh, so much for taking half the time. It is interesting, though. So more gravity is caused by the slowing of time and more mass? How exactly does more mass make time slow down?
Nit pick as much as you like. As I similarly stated before, I have a very, very crude knowledge of gravity. Any information you can give is welcome. |
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propionaldehyde is offline
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05-12-2010, 09:04 PM
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No. Density is not related to gravity. Only mass is.
More gravity is not caused by the slowing of time. Gravity is not caused by time. Gravity is directly related to mass though it is not clear what causes what.
I would say a force of gravity is an illusion. What does gravity do to things? It slows down time and curves space.
Your questions are simple, but as the answers are so complex that nobody knows them, yet. It is pretty irrational for you to feel stupid about a subject so few understand. I don't think that physics class will help you with understand relativity theory at all, but it should still be a good time. |
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admittedheretic is offline
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05-12-2010, 10:13 PM
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Well, since density increases with mass, I was thinking the mass of an area that is more dense would be greater, thus leading to more gravity in those particular places.
After seeing a few videos, it's starting to make more sense. Although I still don't understand how it would slow time. I'll watch some more videos, though.
Well, it's required for a medical degree anyway, so I have to take it whether I want to or not. |
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propionaldehyde is offline
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05-12-2010, 11:31 PM
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Density doesn't necessarily increase if mass is increased. D=M/V
The more you understand it the more sense it shouldn't make at first. Once you've watched a bunch of videos and picked up on the jargon you might consider reading (or listening:audio books) books on the matter that will explain it in further detail. I surely think it is fascinating. The best advice is really to hear out many different authors because they all use analogies that create the potential for misconception, but if you learn enough of the analogies the larger picture will make sense. |
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admittedheretic is offline
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05-13-2010, 12:57 AM
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In addition,
Gravity is one of the most bizarre forces. It is universal (anywhere you find mass you will find gravity), yet its exact cause is not known. It's effects are known (and we can predict and calculate them mathematically), but there's no real explanation beyond the theoretical as to why they occur.
Last edited by Vagrant; 05-13-2010 at 01:31 AM.
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05-13-2010, 07:33 PM
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The simplest working model of gravity (Newton's) states that all bodies in the universe attract each other with a force proportional to the product of their masses divided by the square of the distance between them (the "inverse square law"). Einstein's General Theory of Relativity is much more complicated than this, but for relatively weak gravitational fields (like the one at the surface of the Earth) it is very well approximated by Newton's equation. Measurements show that, on average, at the surface of the Earth, plugging in the right numbers happens to result in a value of about 9.81 m/s^2, but there is nothing at all fundamental about this number. Also, the Earth itself is not uniform in either radius or mass distribution, so the local strength of the gravitational field does vary in both strength and direction -- see
Yes, in part. For exactly this reason (among others, like temperature variation), the surface of the ocean is not flat. It is tilted in part by the fact that undersea mountains are denser than water, so the mountains are more massive than equivalent volumes of water, which causes them to have greater gravitational pull on the rest of the water. Radar altimeters can use this effect to crudely map the ocean floor by measuring subtle variations in sea surface height relative to an ideally smooth ellipsoid (
Sadly, prepare to be disappointed, at least in part. Understanding things like gravitational waves and what the heck "curvature of space-time" means requires General Relativity, which is an advanced graduate class not even all physics Ph.D.s have to take. Newtonian gravity and how the 9.81 varies from planet to planet, on the other hand, requires only high school physics.
This is true of most physics discovered since the late 1800s. An aphorism generally attributed to Neils Bohr, one of the inventors of quantum mechanics, states that "Anyone who isn't confused by quantum mechanics doesn't really understand it." Much the same is true for relativity, at least for the first few decades of study. |
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rbc is offline
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05-13-2010, 09:42 PM
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That is kinda' sad. High school physics is basically all I know. Though I will be taking this next physics class in college, it probably won't be much different. Maybe I'll just take those advanced classes as a little bonus.
Last edited by Synamon; 05-17-2010 at 07:31 AM.
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propionaldehyde is offline
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05-14-2010, 07:26 AM
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I heard that by M theory gravitons travel from other branes into our universe and is what produces gravity here (at least partially). Yes or no? If that would be the case then different empty space should give more or less gravity fields than others independently of the mass of the objects or lackthereof, right? (as it would seep from dense areas on the other brane) This could be measurable if so! (just my own pet theory). |
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05-14-2010, 09:17 AM
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Gravity doesn't emerge in completely random places though. Changes in gravity along the Earth's surface are because the Earth is not an absolute, homogenous sphere. To put it in perspective, a ball bearing from NASA blown up to the size of Earth would have the highest mountains of 2 feet and the lowest valleys of 2 feet. In addition, a ball bearing does not have shifting magma in its core and plates moving around, nor large deposits of various minerals.
Last edited by Synamon; 05-17-2010 at 07:31 AM.
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Vagrant is offline
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05-18-2010, 07:15 PM
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No, M theory still says gravity is the attractive interaction between masses or other energy concentrations. However, it does say gravitons (which correspond to closed loops of string) can leak out of our membrane into other dimensions, which the other forces cannot (since their particles, such as photons and gluons, correspond to open strings, which must keep both of their ends on the brane). Actually, this provides an important constraint on how a universe like ours might be modeled in the theory -- since experimental tests of gravity are extremely strict, there must be something preventing this graviton leakage from occurring. The standard answer is to say that the other seven dimensions are curled up immensely small (as much smaller than an atom as an atom is smaller than the planet). Other, newer suggestions have been made, some of which offer alternate ways to explain the observation that the universe's expansion is accelerating.
This idea is as old as Einstein's gravity theory. One of the parameters in his equations, known as "the cosmological constant", is most directly interpreted as the amount of gravity produced by the mere existence of a unit volume of empty space. Only fairly recently have we actually measured the value of this number, but there is no accepted explanation for why it has the value it has. There are lots and lots of guesses, but most of the simple ones get the number wildly wrong.
It is a good idea based on the many bad translations that have been made for laymen, but they've left out all the reasons it doesn't work quite that way. |
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05-19-2010, 03:07 AM
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The gravitational pull exerted by any given point would vary with the mass of that point. It makes sense that density is a contributing factor. Imagine if the earth were put in a block of Styrofoam. Objects at the edge of a face on the block would have less of a gravitational pull directly toward that face's normal than would objects at the center of a face on the block. Objects at an edge of the block would actually feel a diagonal force toward the earth. Similarly, standing on a less dense area of earth translates to being in a weaker gravitational field, because there is less mass below you. We know from seismic readings that the earths composition is very non-uniform. I think it's very plausible that the variation in pull is due to a variation in density. |
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05-19-2010, 11:45 AM
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I don't see the need to evoke Einstien's gravity to analyse this issue, the differences between it and Newton's gravity is not measurable for the masses we are dealing with.
As for difference's of g on the earth's surface, I'd expect most of it can be explained by difference's in height and the fact that earth is not perfectly spherical. Calculate g for sea level and for the top of everest and I think the difference is about 0.02. Using vector calculus you should be able to calculate a difference for g at the equator and at the poles as well. Differences in density could play a factor as well, but most variations can be explained by the inverse square law. Finally, as for making a facility with a higher gravity, the easiest method would be to just spin the entire facility. The body can't tell the difference between a gravitational force and a force do to centripetal acceleration, so by spinning the facility and putting your floor on an incline you'd acheive the same effect as actually increasing the force of gravity. |
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SirJac is offline
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05-19-2010, 03:59 PM
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I was considering this as well, but it seems unlikely that scientists wouldn't be careful to account for that. |
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rufsketch1 is offline
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05-19-2010, 04:28 PM
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We do if there is need for that much precision, but for most purposes 9.81 is good enough (~0.2% error). |
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SirJac is offline
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05-20-2010, 07:10 AM
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No no. I'm aware of that already. But if there is some unaccounted for discrepancy in gravitational pull, it seems like height above sea level and latitude are the first things one would adjust for. Whereas underground geological density would be extremely tricky to figure out. |
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05-20-2010, 11:10 AM
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In an abstract literal sense density is a factor in the variation of gravity surrounding Earth, but I wasn't speaking with regard to that inquiry at all. I was saying more general that gravity is related to mass and being that density is mass over volume, if volume and mass are increased though the former more so, gravity will still increase though the density will be less. As to answer the question, does more density mean more gravity? No. |
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admittedheretic is offline
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05-20-2010, 01:31 PM
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You could account for the discrepancy in the value for g is due to the difficulty of measuring the gravitational constant. It's been historically a very hard constant to measure and so has a fair chunk of error associated with it. There is also evidence that it's not "constant" at all. |
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SirJac is offline
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05-20-2010, 04:55 PM
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These measurements are from the same geographic location? |
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rufsketch1 is offline
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05-20-2010, 05:22 PM
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You're right, there's no need. However, the OP mentioned gravitational waves, which I why I started talking about general relativity -- mostly in trying to point out that, while way cool, it is irrelevant to the basic question at hand.
Yes! That's the way to do it.
The traditional way to do this experiment is about 200 years old: |
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rbc is offline
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05-20-2010, 06:28 PM
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Yes, these were all measurements done at the University of Colorado. They use an object of known mass (0.5 metric tonnes) and measure the horizontal displacement caused by its gravitational feild for an object in free fall using lasers. The paper on their measurements can be found
That is quite interesting, I'm definately going to have to read and think more about that little tidbit. |
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