# Two protons are separated by a ceratin distance. What should be the distance so as to balance their weight? [closed]

I never got the concept of 'balancing the weight'. This question is from electrostatics, and it's come for a proton and electron too. I would just like to get the concept cleared, because I have the written answer- just don't know why I did what?

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Welcome to Physics.SE. I'm going to close this consistent with our policy on basic homework-like problems. Presumably they want you to compare the force between them due to gravity (i.e. their weight) with that due to electric repulsion. The results should serve to illustrate a point about the relative strength of the forces that many people find surprising when they first encounter it. – dmckee May 6 '12 at 13:16
@dmckee- thanks(even though u closed the question), but what I've done is equalised coulomb's law and the formula for weight (mg), then cross-multiplied to get 'r'. But which proton are we considering? That's what I don't get! – neetprep May 6 '12 at 13:32
Ah. Protons are identical and Newton tells us that the force on one due to the other is equal and opposite of the force on the other due to the one. So pick either one. – dmckee May 6 '12 at 14:09
It occurs to me that they may mean to cancel the weight of one of the protons in the Earth's gravitational field, in which case you want to consider the force on the upper of two protons arranged vertically. – dmckee May 6 '12 at 14:21
The question is nonsense. In case of homogenous gravitational field, you can balance only weight of the upper proton. In case one wants to balance their mutual gravitational field, there is simply no solution as both electrostatic and gravitational force scale with $r^{-2}$. – Pygmalion May 6 '12 at 15:49

## closed as too localized by dmckee♦May 6 '12 at 13:16

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