The five thousand billion freely moving electrons in a penny repel one another. Why don’t they fly off the penny? The shell of the penny prevents...

1. The penny doesn't really have a "shell" - even if it
did, it would be composed of atoms, just like the rest of the penny. The shape and
structure of the macroscopic structure doesn't really influence how the electrons behave
in this case.

2. The electrons do not attract each other;
they are all negatively charged, and like charges repel.

3.
Electrons do not "jam" because they repel one another; jamming would require that they
come into physical contact, which does not happen at these
energies.

4. It's true that the electrons don't have enough
speed to escape the penny - however this is not a complete description of what is taking
place. The electrons are being influenced by another, stronger
force.

5. The electrons are attracted to the
billions of positive charges in the protons. The electrons would need a significant
amount of energy in order to overcome and escape this
force.