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Given that the electrical force is so much stronger than gravitational force at atomic levels, why is it that it's the gravitational force between you and the earth that keeps you on the ground rather than the electrical force between you and the earth?

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hint: which electrical force? –  Tobias Kienzler Jan 25 '11 at 7:03
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Please note that the "homework" tag does not solely indicate problems that someone is actively trying to solve for their next problem set. Problems for exam review or problems encountered in a textbook during independent study are also considered "homework" meta.physics.stackexchange.com/questions/234/… –  Mark Eichenlaub Jan 25 '11 at 8:54
    
Nope not studying for an exam either-semester just started. I was intrigued by something so I asked it. Apparently WIMP is the only one that really knew the answer-the rest of you guys just spent all your time trying to argue rather than answering questions. You lose nothing by answer this question whether its homework or not. Obviously you guys are just trying to argue about something and attempt to gain authority over this site. Last I checked it was run by the community. I am part of the community. If I claim its not homework, then its not homework. –  maq Jan 25 '11 at 21:28
    
The tags are not for your benefit. They're for everyone else's benefit as they sort through the questions. That means the questions should be tagged according to their content, not according to the asker's whim. Regardless, this has become a meta discussion so if you want to continue it, we should do it on the meta site. –  Mark Eichenlaub Jan 26 '11 at 9:16

4 Answers 4

up vote 10 down vote accepted

Because there's no negative gravitational mass. Electric charge can be neutralized, gravitational attraction not.

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Actually, if you were at rest on the ground, the van der Waals repulsion between the atoms of the soles of your feet and the atoms of the ground — which is electrical in origin — exactly cancels the gravitational force between your entire body and the entire mass of the Earth.

Imagine that!

And the van der Waals force isn't even a direct Coulomb force between two simple charges, but a much weaker indirect electrical repulsion between neutral atoms due to a deformation of the electron clouds. I know you might argue the repulsive van der Waals force is actually due to the Pauli exclusion principle, and that is also true. After fixing the positions of the nuclei, the physical ground state — which is given by a totally antisymmetric electron wavefunction — has a higher energy than some unphysical electron wavefunctions which aren't totally antisymmetric. But if we restrict ourselves to the physical wavefunction, the immediate repulsive force can still be traced back to electrostatics.

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I assume we are not supposed to give direct answers to homework questions. If I'm wrong I'll be happy to edit this.

Mohabitar, to answer this you should consider what properties of an object cause electrical forces to be exerted on it. Do you posses these properties under normal circumstances? What about the same question as applied to gravitational force?

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You're absolutely right that we should avoid giving direct answers to homework questions. –  David Z Jan 25 '11 at 6:42
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Eh you guys are annoying about HW. This is not homework. It something for us to think about. I also said previous, meaning it was for a previous semester lab, also meaning I ask this question because I am curious, not because I need the answer. –  maq Jan 25 '11 at 6:45
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@Mohabitar: I'm not trying to be annoying, I'm trying to follow the conventions we have established as a community. It's not something I did to be rude to you. –  Colin K Jan 25 '11 at 6:48
    
No I understand. I've been using this site since the first day it was launched, and everytime I asked a question, it was such a pain to get anything near to an answer. An answer is not even what I want sometimes, but if you want to give hint, then give a reasonable hint. I think you guys (people who answer questions) try way too hard to play the 'teacher' role. This is a virtual environment. We cant play give and take for 12 hours like we can in a face to face conversation. It just doesnt translate to the online world. The format is messed up, and I find it very hard to benefit from any posts –  maq Jan 25 '11 at 6:53
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@Mohabitar: Well I don't want to get into a long discussion in comments, but you should understand that this site was made for relatively high level questions. When you ask questions which are basic even at an undergraduate level, you probably won't get the result you were expecting. What seems a very obvious and useful hint to most of us may not help you much, but that is because the people here tend to be practicing scientists or engineers. Personally, my hint seems quite reasonable and I don't see how you could read it and still not see the answer. –  Colin K Jan 25 '11 at 7:14

You write "rather than the electrical force between you and the earth". There is no electrical force between you and the earth because neither of you is charged! But you and the earth do both have mass so gravity acts but electricity doesn't.

"that the electrical force is so much stronger than gravitational force at atomic levels'" is only true between two charged particles of say the mass of a proton and the charge of a proton.

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