
178 Questioning the Universe: Concepts in Physics
14.6.1 TWO CLASSES OF MATTER PARTICLES
Note that in the description above, electrons were not indicated as being composed
of quarks. They are not. In fact, they, and other particles like them, form a separate
class of fundamental particles known as leptons, which is derived from the Greek
leptos, meaning “ ne” or “small.” They interact via the weak nuclear force. Since
some of them are charged, like the electron, they also interact via the electromag-
netic force. Figure 14.5 shows a chart of the quarks and leptons. Let us consider the
similarities and differences between these two types.
14.