is it easier to negatively charge something than to positively charge it?

Interesting. If you had, say, a ping-pong ball sized solid aluminum sphere, sucking all the electrons out scales to a voltage roughly in the 1e12 kind of turf. As a practical matter, it would come apart long before you could charge it that much. Atoms get ripped out of metals at much lower field strengths.

And after all, it's electrons that hold things together.

John

Well, you could just as well give an object a positive charge by putting protons onto it, or positive ions. The difference is that the mass of a proton is much greater than -- about 1840 times -- the mass of an electron.

You might also want to consider practical limits. A "pile" of electrons, or a "pile" of protons, will try mightily to get away from each other. I believe the capacitance of an electrically conducting sphere 1 meter radius in freespace is 111.3pF, more or less. So if you put a mere 1 coulomb of electrons on it (if you could actually do that), about 6*10^18 electrons, it will have a potential of nearly 9 billion volts. Left as an exercise for the reader: what's the electrical field strength immediately outside such a sphere? What keeps the excess electrons on the sphere?

But protons don't like to hang around. Conservation of charge works, but physics being funny like it is, 13.6eV says those protons will grab up electrons, forming hydrogen which goes on its merry way, leaving the target electron-deficient. Depending on the material, some may chemically combine (I guess you could say a proton beam is the most acidic thing known to science, it's the ultimate Bronstead-Lowry proton donator), which you'd have to figure out in isolation of the charge. I suppose the way to tell would be to measure its mass extremely accurately, comparing equal charge (easy to measure) obtained by electron vs. proton bombardment. (Note that, at the charges we're talking, relativity will have a measurable effect. Assuming such apparatus that can actually measure these differences.)

Tim

Good answers, thanks everyone.

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As has been pointed out earlier in this thread, you can't put much charge on a physical object before the mechanical forces generated by self-repulsion pull it apart. Thinking about protons as Bronstead- Lowry acids in this context is a pure waste of time.

-- Bill Sloman, Nijmegen

Well it was an aside, hence the parenthesis. You're welcome not to read it (which is what parenthesis mean).

Tim