proton of a hydrogen atom
"Metaphors related to everyday things like cars or sports help get the point across. For example, if the proton of a hydrogen atom is the size of, say, a volleyball, then the electron is a spec of dust about 11 miles away."
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.