This Instructional Activity is a part of the Lesson 12, Unit 1, Grade 8. Remind students that a kilogram is 1,000 grams, so we can quickly write the masses in the new unit using our knowledge of powers of 10. Now let's look at the field of particle physics or the study of subatomic particles, such as protons, electrons, neutrons, and mesons. In the previous lesson, we worked with the masses of protons and electrons.