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Author | Topic: Throwing Stuff Down A Mineshaft | |||||||||||||||||||||||
Parasomnium Member Posts: 2224 Joined: |
And taking this massive-concept to a hollow sphere... if it were massive enough, it would pull your body apart and splatter you all over the inside walls I'm not convinced that this would be what happened. If the forces from all sides cancel out, as you explain, then the net force on you would be zero. The rest of what you say makes excellent sense. "Ignorance more frequently begets confidence than does knowledge: it is those who know little, not those who know much, who so positively assert that this or that problem will never be solved by science." - Charles Darwin. Did you know that most of the time your computer is doing nothing? What if you could make it do something really useful? Like helping scientists understand diseases? Your computer could even be instrumental in finding a cure for HIV/AIDS. Wouldn't that be something? If you agree, then join World Community Grid now and download a simple, free tool that lets you and your computer do your share in helping humanity. After all, you are part of it, so why not take part in it?
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cavediver Member (Idle past 3671 days) Posts: 4129 From: UK Joined: |
But I was under the impression that you can do the maths for the gravitational effects of any massive object by treating it as a point mass. Only if you are located outside the shell. Once inside the shell, you experience no force whatsoever at any point. There is no "floating" towards the centre. It's straightforward calculus, just integrating hoops from pole to pole.
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cavediver Member (Idle past 3671 days) Posts: 4129 From: UK Joined: |
Inside the hollow part, you have all the tiny points actually pulling you away towards the surface. Given a perfect sphere, each point on one side has an equal point on the exact opposite side that cancels out. Add in a bit of air resistance and no matter where you are in the centre area, you'll eventually "float" to the centre of the sphere. No, there is no tendancy towards the centre, nor any other point. There is zero gravitational force on the test mass inside the spherical shell.
*Note: By "cancels out" we don't mean that the forces go away. It's that the forces are equal-but-opposite. The forces are all still there, and all as strong as they were before, it's just that there's no movement as a result of those forces. Hmmm... if you have two sine waves of enormous amplitude coincide out of phase, would you say that there are are equal and opposite waves at those points, or that there are no waves at those points
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cavediver Member (Idle past 3671 days) Posts: 4129 From: UK Joined: |
I, um.. would like to see the integration on this I'm going to cheat and refer you here as I hate trying to typeset maths at EvC
'm assuming that you're not "weightless" if you're being pulled towards the centre of mass... you just feel like you have very little weight. But the only place you actually feel truly "weightless" would be at the centre of mass, no? No, you are truly weightless, and would be in this state anywhere inside the shell.
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Stile Member Posts: 4295 From: Ontario, Canada Joined: |
cavediver writes: I'm going to cheat and refer you here Ah yes, thanks for the refresher, that's all I needed to see. Of course, there's more mass on "one side", but it's farther away. And the cool properties of a perfect sphere balance this distance-mass relationship perfectly equally. I understand. Yes, even if you're at a spot 90m from the centre (back to my scenario), you wouldn't move due to any gravitational forces, and therefore be weightless.
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Stile Member Posts: 4295 From: Ontario, Canada Joined: |
cavediver writes: Hmmm... if you have two sine waves of enormous amplitude coincide out of phase, would you say that there are are equal and opposite waves at those points, or that there are no waves at those points Perhaps I am simplifying gravity too much. I take it the gravitational forces act via waves, then? I was thinking more like if I have a force of 10N pulling my left arm and 10N pulling my right arm, I don't move (they "cancel out"), but both forces are still there. Am I simplifying gravity too much then, by reducing it's force to a mere number of "x Newtons"?
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Larni Member Posts: 4000 From: Liverpool Joined: |
Thanks for clearing that one up, Stile.
I really must stop thinking, now: my head hurts
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Larni Member Posts: 4000 From: Liverpool Joined: |
How wonderful that we can get from goats to Dyson spheres in less than 40 post.
EvC is a really odd place
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Blue Jay Member (Idle past 2725 days) Posts: 2843 From: You couldn't pronounce it with your mouthparts Joined: |
Just to let all the creationists at EvC know, this is what scientists do in their spare time.
I'm Bluejay. Darwin loves you.
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Stile Member Posts: 4295 From: Ontario, Canada Joined: |
No problem, but make sure to read my Message 35 in this thread, I'm pretty sure I'm screwing up the "inside the hollow sphere" stuff as cavediver is explaining.
I got carried away and forgot the relationship with mass vs distance. I was thinking of gravity as too much of a "linear force" when it's more of a linear force that has a fundamental basis as a wave. In which case, what I said about the forces cancelling out but still being there is totally incorrect, and the forces would actually cancel out so that there is no "feeling" of them at all. This is not true for energy like Kinetic energy (someone actually pulling on my arm)... but I think Potential energy works a bit different and actually does cancel out down to absolute 0 force as opposed to simply 0 net force. See cavediver's reply to my question and I'm pretty sure he's about to confirm that forces due to gravity act as waves. I should be able to confirm that (I found Newtonian physics extremely intuitive in school), but apparently it's been a bit too long since college for me ..which makes me a bit sad, it's only been 9-10 years
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Stile Member Posts: 4295 From: Ontario, Canada Joined: |
Mantis writes: Just to let all the creationists at EvC know, this is what scientists do in their spare time. Next there'll be a conversation on how much the water level of the ocean changes (if at all) when you throw an anchor overboard...
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cavediver Member (Idle past 3671 days) Posts: 4129 From: UK Joined: |
I take it the gravitational forces act via waves, then? No more or less than any other force. Gravity is great because it is the real deal - a fundemental force that we can see up close. E/M we can too, if we have a pair of magnets. But E/M is behind just about every other force we encounter, whether it is lifting weights, pushing doors, trains pulling trucks, etc. The large scale mechanical forces are simply infinitely tangled webs of electromagnetic interactions of which we have no awareness. And fundemental forces simply come down to numbers. What is the force's value at this point in space. At that point, there is no way to tell whether a value of +15 is made of +25 and -10, +1000000000000015 and -1000000000000000, etc.
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Parasomnium Member Posts: 2224 Joined: |
cavediver writes: Parasomnium writes: But I was under the impression that you can do the maths for the gravitational effects of any massive object by treating it as a point mass. Only if you are located outside the shell. Once inside the shell, you experience no force whatsoever at any point. There is no "floating" towards the centre. It's straightforward calculus, just integrating hoops from pole to pole. Thanks for enlightening me, Cavediver, I didn't know that. If I'm correct you're a physicist of some kind (I'm too lazy to look it up in old messages), so I'll take your word for it. "Ignorance more frequently begets confidence than does knowledge: it is those who know little, not those who know much, who so positively assert that this or that problem will never be solved by science." - Charles Darwin. Did you know that most of the time your computer is doing nothing? What if you could make it do something really useful? Like helping scientists understand diseases? Your computer could even be instrumental in finding a cure for HIV/AIDS. Wouldn't that be something? If you agree, then join World Community Grid now and download a simple, free tool that lets you and your computer do your share in helping humanity. After all, you are part of it, so why not take part in it?
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Stile Member Posts: 4295 From: Ontario, Canada Joined: |
I think I understand... let me ramble a bit and if you could confirm what I'm saying it would be greatly appreciated.
All forces act in the same manner.Forces seemingly cancel each other out as waves would do when they act on the same "spot". Forces due to Gravity (Potential energy) act "everywhere" (in their mass vs distance relationship). Forces due to Kinetic energy act locally on the spot they interact. I think that was my confusion. The force of gravity being "everywhere" vs. local forces due to something's mass running into something else's mass. All forces act the same, but if I have a planet's gravity pulling on my left and an equal planet's gravity pulling on my right... I don't get ripped apart between the two because the "everywhere" force due to their gravities actually cancels out. All forces act the same, but if I have a truck pulling on my left and an equal truck pulling on my right... I get ripped apart because this Kinetic energy is focused locally on my arms, which itself comes down to fields interacting. However, the interactions of these fields are more local and not so pervasively "everywhere" such as the interaction due to a gravitational force. Something like that?
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DevilsAdvocate Member (Idle past 3129 days) Posts: 1548 Joined: |
No more or less than any other force. Gravity is great because it is the real deal - a fundemental force that we can see up close. E/M we can too, if we have a pair of magnets. But E/M is behind just about every other force we encounter, whether it is lifting weights, pushing doors, trains pulling trucks, etc. The large scale mechanical forces are simply infinitely tangled webs of electromagnetic interactions of which we have no awareness. Correct me if I am wrong but isn't the reason that gravity acts at a more macro scale than the other fundemental forces i.e. weak, strong and electromagnetic is that gravity acts in one direction i.e. attraction and does not cancel itself out? Yes, gravitational forces from matter can effectively nullify the gravity forces from other matter resulting in effectively a near 0 g effect but this is not the same as an attractive and a repulsive force i.e. electromagnetism cancelling each other out on the microscopic realm resulting in a very short range of reaction with matter. Hope this makes sense. For me, it is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring. Dr. Carl Sagan
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