That is, given enough time by itself, one unstable particle will fly apart into two or more particles. By carefully observing and logically classifying these decays according to some well-understood laws of nature, particle physicists have been able to explain much about the fundamental structure of matter. They don't seem to change into other particles over time, which is to say they don't decay. Most other particles have dominant decay modes. They decay into one combination of particles more often than into other combinations.
Many particles also have rare decay modes.
If you have the patience to watch a million or so decays, you might see one of these combinations. Each of the three activities below starts with a page of suggestions and background information for the teacher. The second page is a brief introduction for students. Whenever you run across an unfamiliar word related to particle physics, please refer to A Glossary of High-Energy Physics Terms , produced at Boston University's physics department. This page leads you to a clickable table of 39 particles, most of which had been discovered by the 1960s.