# Atomic Glue

### Mike Jensen

Posted May 5, 2010

Being an electrical engineer, occasionally I like to review the fundamentals of electricity. Kind of fun to see what I remember, but even more important, to see what additional insight a few years of experience might bring to how I view basic engineering facts. I consistently have “Aha!” moments where something I learned many years ago comes into focus, or with more seasoned understanding I know to ask better questions, make better links between what once seemed disconnected facts, or think a little deeper about natural laws that I used to take for granted. Such was the case a few days ago when I dusted off a copy of my high school physics book to review some of the fundamentals behind how electricity works.

A material’s ability to conduct electricity depends on its atomic structure. If you haven’t reviewed your physics in awhile, here is a quick review: an atom’s structure consists of a proton/neutron nucleus around which electrons buzz at dizzying speeds. A classic analogy compares an atom’s structure to our solar system: the sun is like an atom’s nucleus, and the planets orbiting the sun are like the electrons orbiting the nucleus. A bit of a simplistic view, but good enough for the discussion at hand. With this as background, consider these points:

1. To recap the paragraph above…we know that all matter is made of atoms, and atoms are collections of protons, neutrons, and electrons. Protons and neutrons form the atom’s nucleus, and electrons whirl around the nucleus at different energy levels.

2. We know that protons have a positive charge, electrons have a negative charge, and neutrons are, well, neutral.

3. We know that like charges repel each other, and opposite charges attract.

So here is my “thinking a little deeper” moment: if the nucleus of an atom is made up of only protons (positive charge) and neutrons (neutral charge), and given #3 above, what’s the glue that holds the protons and neutrons together? Shouldn’t the positively charged protons in the atom’s nucleus repel one another? I’m sure a teacher or professor, at sometime in my academic history, explained why the protons play nicely together, but I don’t recall the explanation. And really, this is a level of detail that most engineers don’t need to worry much about. We may have learned the reason in Physics 101, but there wouldn’t be much of a reason for it to stick – too many other things to worry about in the world of widget design. But with the mystery a-foot, I needed to find an answer, so I first sent an email to my soon-to-graduate-from-college son, a biology and chemistry major. He’s pretty sharp, particularly in the sciences, and his brain cells are much newer than mine.

Funny thing…even my son had to dig a bit through his memory engrams (needless to say, I didn’t feel so bad since my last official physics class was over 2 decades ago). Even though he was a little fuzzy on the details, he explained there is a form of atomic level glue called “the strong nuclear force” which holds atomic nuclei – the protons and neutrons – together. It turns out that the ability of the strong nuclear force to hold an atom’s nucleus together trumps the protons’ natural tendancy to push themselves apart, at least for very close distances on the order of a proton’s diameter. If the spacing gets much larger, the electromagnetic force takes over and the protons go back to repelling one another. Click here to read a bit more.

Will knowing about the strong nuclear force make me a better engineer? Probably not. It’s at a level of detail I don’t normally deal with. I’m more concerned with analyzing how components interact with one another when connected in a larger mechatronic system. But every engineer, regardless of discipline or technology, has components to play with precisely because the strong nuclear force keeps atomic nuclei glued together and well-behaved. Even when natural behavior seems to contradict what I think I know, there is usually a reasonable explanation, even if I have to dig into the fundamentals of particle physics, courtesy of my high school physics book, to find the answer.