WHy don't the electrons fly off.

[JimBoot]

So why don't they fly off?

This is from Michael Clarage's newsletter.
I attended a lecture by Andre Assis, hosted by Matt Ehret of the Rising Tide Foundation. The topic was the fundamentals of static electricity. Andre bravely demonstrated several experiments of zoom, masterfully navigating camera angles, juggling plastic rods and coffee cups filled with plaster and Dandelion fluff and beautifully simple electrostatic devises made from various grades of paper.

At first I was wondering about the pace of the presentation. Andre was carefully showing how when you rub a plastic rod, then approach a piece of paper suspended from a string, that the rod & paper attract. OK. Maybe not everyone has done this many times, but I certainly have, and I am guessing most people on the meeting have also.

But then he took the proverbial right turn, and showed how different materials actually behave under these circumstances. Our usual conceptions of insulator & conductor are woefully inadequate. Many substances, like rubber and paper are perfect conductors in certain voltage regimes. So you can throw out all the little grids you learned in school about what substances are insulators or conductors.

I was thrown off balance at the end of the lecture, when Andre presented the usual picture of the charged rod, or charged sphere


We rub a plastic rod with wool, and WE ALL KNOW that electrons are deposited upon the plastic rod. Do we? If all the excess charges are on the surface and want nothing more than to fly away from each other... then why don't they fly off? What holds them on the rod? I found my brain thinking mechanism stop and go tilt. Well, an electron can't fly off because... because there must be something holding it on... like a Coulomb force... but we just said that the Coulomb force on each electron was directed outward... TILT

I have resisted the impulse to consult the internet on this one. I think it is worth pondering for a while on my own.

Andre has several books on the fundamentals of electricity. As is so often the case, his excellent work is under appreciated because it can't be easily integrated into the standard curriculum. https://michaelclarage.substack.com/?r=5nc1wo&utm_campaign=subscribe-page-share-screen&utm_medium=web

[Allcanadian]

My go to book I bought 20 years ago was A.D.Moore "Electrostatics--Exploring, Controlling, and Using Static Electricity"

We rub a plastic rod with wool, and WE ALL KNOW that electrons are deposited upon the plastic rod. Do we? If all the excess charges are on the surface and want nothing more than to fly away from each other... then why don't they fly off? What holds them on the rod? I found my brain thinking mechanism stop and go tilt. Well, an electron can't fly off because... because there must be something holding it on... like a Coulomb force... but we just said that the Coulomb force on each electron was directed outward... TILT

Your not wrong in your thinking and relates to something called a charge mosaic which was discovered fairly recently.

Charge mosaics in electrostatics refer to the non-uniform distribution of electric charge that can develop on surfaces when materials come into contact and then separate. This phenomenon can result in areas of opposite charge polarity on the same surface, which has puzzled scientists for years.

In simple terms, we can have layers of different charges on a surface with many electrons forced together in clumps. This gives that specific area a net (-) charge even though there could be many (+) charges below or around the clump holding them in place. The term net just means more of one kind of charge than the other in an area. The term charge mosaic relates to how tile mosaics are laid out.

In fact, much of what we thought we knew in the last 100 years was incorrect. The surface charge is not from rubbing only contact and the charges are non-uniformly distributed. We used to think the net charge was more like a thin layer of uniform charges on a surface but this was incorrect.

[chief kolbacict]

Electrons fly away very well from the tip of the needle.
The smaller the radius of curvature of the sphere, the better.   

[F6FLT]

...
If all the excess charges are on the surface and want nothing more than to fly away from each other... then why don't they fly off? What holds them on the rod?
...

They want to, but they don't have enough energy, a question of "work function" https://en.wikipedia.org/wiki/Work_function.

Whether it's to escape into the vacuum, or worse, to move across the surface of an insulator that is full of obstacles at the electron scale, they would need much more energy. Even the cathode of a vacuum tube, while the anode's field attracts them and the vacuum is not an obstacle, must be heated in order for the electrons to leave it.

It's like a drop of water under a horizontal plate. It wants to fall but doesn't have enough energy; its weight is not enough to overcome the interfacial adhesion forces.