I was watching one of the Science Posts this morning, and it made me think back to the good Teachers I had back in the day. Some of their lessons I have never forgotten. Even today, I use some of their techniques to teach basic things to my grandchildren. Like the difference between Nuclear Fusion, and Nuclear Fission. This is what my Teacher told me way back in the early sixties. It is still an effective way to picture the difference between Fusion and Fission. Here goes:

"Everyone take out a sheet of paper. ( We all did.) Now, I want you to fold it in half. Now fold it again. And again. And again (and let me tell you that fourth fold was a bit harder to do.) And again."
That fifth fold was tough. By the sixth fold, not many could even try and make another fold. I don't think anyone made a seventh fold. So we all stopped folding with these solid chunks of paper maybe an inch square clutched in our little hands.

"Now, I want all of you to try and rip that folded square in half."

We tried. Even Rich Adams, who was the center on our Football Team and as strong as a horse, couldn't even get a tiny tear to appear. There was much laughter, and quite a few comments about things like: "What the heck? It is only paper!" "We need scissors...no..we need a bolt cutter."
Finally we all gave up.

Then she told us this simple statement:

"When you folded that paper, each fold increased the energy. There was no strain, no effort, until the very end. You now have a nice neat package that is very strong. When you tried to rip it, you could not. Because all that energy is stored in the folded paper. If you could be strong enough to rip it apart, there is no way you could control your hands and arms, they would just fling apart in any direction because of the amount of force you needed to rip the paper."

Then the explanation - which I remember to this day:

"Folding the paper was like Fusion. Link after link. Controlled and clean. Ripping it apart, unable to control what happens, is like Fission. Tearing the links apart with obscene amounts of power. Uncontrollable and dirty. "

No math. No formula's. Just a simple way to get a peek at two very different and very powerful concepts. No wonder we never worried about Grades in her Class. We just liked learning stuff.