During the "nukular" 80s I had a fair idea of the power of an 'atom bomb', but couldn't figure out why it was so darned big when I'd been told in school that an atom was a really really really small part of the universe.
A childhood belief about physics

others believed things like this
- I used to believe that an atom bomb was a dragon in the sky.— Mazzkitten
- I used to believe that "euthenasia" was "youth in Asia", and I couldn't figure why that was A Bad Thing.— Kellye
- when I was little my uncle told me he was part bear. I believed people could be part bear until I was twelve. — Audrey
- I used to beleive that the moon was where the local fair was.— tah
- I used to believe that at the end of the universe was a big plywood wall.— matt
- I used to believe Sting was my dad in a parallel universe — Jenn Green